Technically Maybe Yes, But No
In the 40k universe you don't have to worry about protein compatibility or a host of other "hard science" reasons why things which evolved separately on different planets would be mutually indigestible. Either the Old Ones made everybody out of the same underlying structure or handwavium has been applied. So the question then becomes, is it doable from a "can we eat that sort of plant" level? The answer here is more ambiguous.
We know from Book 2 of the Ragnar Blackmane series that Orks can be eaten by space marines, as one marine munched on an ork so a marine can drive a trukk via his Omophagia gland. (They aren't specific as to how much, but traditionally part of a creature's brain gives best results.) There are similar references scattered around to marines eating ork as well. Of course a Space Marine can ingest things that would kill a normal human (Mjod comes to mind) so this isn't perfect proof.
The real problem comes with Ork physiology. It's not an animal, it's an amalgam of fungal and animal properties. When one dies, its body releases spores. These spores, if they land in the right area, will spawn not just orks but EVERYTHING IN ORK SOCIETY. So Orks, gretchin, squigs, snotlings, and a whole host of other things. These "things" go down right to the microbial level apparently, as the Tyranid vs. Orks Octarius War is described as occuring "down to the microscopic level." What's more, the ork spores are described in the Octarius War blurb as "aggressively spreading." I think it's this last bit that puts paid to the idea of humans ingesting ork 'meat' in any meaningful quantity.
Even assuming that the fungus/meat is digestible by a human, there's the chance that these "aggressively spreading" ork microbes will get into your body along with the cooked meat. Medium rare orksteak? Congradulations you have spores. Given that they're described as being "at war" with tyranid microbes I don't think we can assume the human digestive system could handle them, and what that means for the poor person who ingested the meat I can't say. *
- There doesn't seem to be any precautions taken by imperial guardsmen when they fight orks when it comes to spores. This might be an indicator that ork spores aren't as dangerous as we're led to believe by their description in the Octarius war. However units like the Armageddon Steel Legion which are depicted as fighting orks over long periods DO have masks/rebreathers. Other units (the troops deployed to armageddon's jungles in Codex: Armageddon come to mind) without respirators which fight orks for long periods do seem to go a bit... feral. Almost Orky. While it's depicted as a sort of "become like your enemy" mental thing, who's to say it's not due to ingesting/inhaling large amounts of ork spores which go on to mess with your mind?
The biggest "no" I can think of though would be cultural. The Imperium Doesn't Do Xenos. Xenos are polluted and evil and sinful, why in the name of the Emperor would you willingly place some of that pollution and sin inside your own body? The imperium doesn't even hold with Xenos crops, so why would they ever want you to eat an alien? (there's a lovely bit about it in Traitor General where 'xenoagricultural' stuff is considered unclean and not fit for consumption even though it's not, strictly speaking, chaotic in nature.)
At the end of the Day Rogue Trader is no longer considered canonical, and I think without clear and exact references to a bit of RT fluff in the more recent fluff we have to conclude it is no longer considered a thing. Especially when it goes against the grain as much as ork burgers do. Which is a shame, because I would LOVE to see an agri-world that produces Ork/squig paddies as their primary foodstuff.