The Baron's original plan was to put Pityr De Vries (it's been some time since I read Dune, so apologies if I got that name wrong) in charge of Arrakis, as he'd do an excellent job of squeezing all possible revenue from the planet. Remember that Vladimir Harkonnen's long-term plan was to marry off Feyd-Rautha to Princess Irulan, thus ensuring the Imperial throne for his nephew; he needed the great wealth of Arrakis for the necessary bribes and other expenses that would be incurred in organising such a marriage, particularly given that every other family in the Landsraad would want Irulan's hand for their own sons and nephews. When De Vries got himself killed by Duke Leto, Baron Harkonnen was forced to turn to his elder nephew, Glossu (Beast) Rabban. Rabban was less-talented than De Vries, so the Baron explicitly instructed him to be very brutal in squeezing every last drop of wealth from the planet and its populace.
This is where the situation becomes more complicated. In his attack on House Atreides, the Baron was fortunate enough to capture Thufir Hawat, the Atreides' Mentat. Hawat was walking the very fine line of desiring personal revenge against the Harkonnens, whilst simultaneously relying on them for his personal survival. He had to offer the Baron plans that seemed workable, while at the same time potentially destroying the Harkonnens. He thus came up with a plan to pit House Harkonnen against House Corrino, the two Houses responsible for the fall of House Atreides, against one another.
His plan was simple; House Corrino had maintained the Imperium for 10,000 years, largely through the military might of the Sardaukar. Whether through espionage or logical deduction, House Atreides had discovered that the Sardaukar were in fact prisoners, or the descendants of prisoners, condemned to life on the Emperor's private prison planet, Salusa Secundus.
As Arrakis and Salusa Secundus shared many similarities, Hawat proposed that the Baron use the Fremen as a substitute for the Sardaukar, thus creating a private army capable of fighting the Sardaukar toe-to-toe. Rabban would treat the Fremen extremely harshly, earning their enmity. Baron Harkonnen would remove Rabban from his position, begin treating the Fremen favourably, and portray himself as their saviour. This would cause the Fremen to grant the Baron their loyalty, and enable him to turn them against the Padishah Emperor; the Baron could then seize the throne for himself. After hearing Hawat's plan, and feeling somewhat chagrinned that he had already mentioned the possibility of using Arrakis as a prison-planet to an Imperial envoy, Baron Harkonnen proposed that Feyd-Rautha be installed as the Fremen's deliverer rather than himself, as he was planning to retire soon.
The possibilities of this plan for the Baron are obvious; he gets his own private army on top of Arrakis' obvious wealth, thus enabling him to directly challenge the Emperor for power. Combined with the possibility of marrying his nephew to the Imperial heiress, the odds of his hand-picked successor becoming Padishah Emperor - and thus the Baron being the true ruler of the Imperium - would increase greatly. The risk of angering the Emperor enough to bring the full weight of the Sardaukar down on himself, as it had been on Leto earlier, was worth the risk.
The possibilities for Hawat are equally appealing; he's setting up House Corrino and House Harkonnen to kill each other. If the Shaddam IV gets wind of the Baron's scheme, he will crush House Harkonnen just as he did House Atreides earlier. AFter all, the reason the Emperor brought about House Atreides' downfall was because Leto I, Lady Jessica, Thufir Hawat, Gurney Halleck, and Duncan Idaho had, between them and with their combined skills, managed to create a small military force hat was, in Hawat's own words, "within a hair's breadth as good as Sardaukar." Any attempt by another House, especially one as powerful as House Harkonnen, to do the same, would bring swift reprisal.
Even more to Hawat's favour would be if Baron Harkonnen actually succeeded in his scheme, at least partly. If the Padishah Emperor found out abut Baron Harkonnen's plan too late to stop it, there existed the very real chance that House Harkonnen and House Corrino might cripple each other in a bloody, brutal conflict to the death. Forget the laws of kanly; with their personal survival at stake, both Vladimir and Shaddam would pull out all the stops, including the use of atomics. Hawat might actually succeed in destroying both Houses responsible for the destruction of House Atreides.
So to answer your question, no, the angle about recruiting Fremen was not part of the Baron's plan from the beginning. You'll recognise that the plan Hawat came up with for the Baron to use was actually the same plan the Lady Jessica came up with for Paul. This was a coincidence; Hawat's goal was to get the Baron, and hopefully the Emperor, to destroy themselves, by playing a very high-risk game, whereas Jessica and Paul had already lost their House; they no longer had anything to lose, and they were already amongst the Fremen. Vladimir did plan on having Rabban treat the people of Arrakis terribly from the beginning, but the reasoning changed when Hawat clued him in on the possibilities of the Fremen. Hawat may also have anticipated that the Emperor would come to Arrakis himself - as he did - to ensure that the Baron's plan didn't work, and that the vengeful Fremen would kill them both. That would suit Hawat just fine as well. He was only interested in living long enough to gain vengeance by that point; the manner of his vengeance didn't matter.
