In the Stargate SG1 universe, there doesn't seem to be animal life on alien human-occupied planets. The only non-plant life encountered are other sentient beings. Does this mean that any humans relocated to the alien planets by the Goa'uld had to subsist on a plant-only diet?
Of course not. There are multiple cases on the series of off-world humans eating meat, though the most notable example is the armadillo-type creature in the feature film.
Now, it is true that we never actually see an off-world human eating meat during the run of SG-1, but we also very seldom see them eating at all. When they are, it is usually a scene, similar to that in the film, though sharing more in common with the similar scene from Indiana Jones and the Temple of Doom, where the team shares a meal with the poor farmers/ miners/ slaves on the planet of the week, which establishes that these people are too poor/ subjugated to have easy access to meat.
This in no way implies that no off-world humans eat meat; the relative good-health of many off-world humans would preclude a non-meat or little-meat diet. It's also very difficult to believe that a high-class human, such as Pyrus in Need, would not be eating meat. That same episode establishes that many planets have similar life to Earth - the joke Daniel's love-interest makes about trees being isolated to her world - which, again, would imply that there are animals worth eating on many worlds.
I do think it is very reasonable to assume that most human colonies were established by the Goa'uld as mining settlements, and it is also probable that any meat products would be confiscated by the local Goa'uld/ Jaffa or a trusted human overseer, as happened numerous times on our own planet (such as feudal lords denying nearby peasants the right to hunt on their property). There is also the problem that many off-world colonies would not have had access to the animals eaten on Earth once the Goa'uld lost control of the planet.
In Sacrifices it is established that the Jaffa have at least one ritual requiring goat meat. A similar creature is eaten in the Pegasus galaxy. The episode Emancipation takes place on a planet inhabited by horse-riding Mongol warriors. While they are not seen to eat horse-flesh on-screen, it is highly-likely they did so, as to Mongolian and Turkic peoples on Earth. The sourcebook for the Stargate SG-1 Roleplaying Game notes that llamas were transplanted from Earth to the human-occupied planet Gallicia, where they are a staple food-source (along with the aforementioned goat). The ability of the Ori-created insects in The Scourge to adapt to an all-meat diet indicates that meat is eaten on other human-occupied worlds as well. In The First Commandment , Carter mentions that it's strange that there are no birds on the planet, which, again, implies that there are birds, which are likely edible, on other planets.
We also can't forget the simple fact that it is a lot cheaper, from a production stand-point, to highlight the wealth of a human by showing them eating grapes, rather than steak, and likewise it is easier to highlight a person's poverty by showing them eating a meagre salad than a strange creature. A regular series episode had a much lower budget than the feature, and what money they had was more likely to be spend on cool CGI effects or battle-sequences.
I think you're reading too much into the lack of spit-roasts on-screen, myself.
However, that is not to say that people didn't eat meat. It might have simply not been mentioned. For example, in the 1994 movie, there were these big yak/camel things (apparently called "mastadge"). What do you think happens when one of them dies? Why not eat them?