If +stat food is a part of someone's build why would you restrict it? Some people build around the fact they will always have +stat food around. If it's only used during a prebuffing phase and not allowed during the actual fight then I see no reason to not allow it.
Is there a reason to give alchemists pots at all? They still have a homunc to attack with and now you give them the ability to keep themselves and the homunc alive forever. Just because they don't have AD doesn't mean they should suddenly be allowed to use pots. It's not an equal exchange at all. I guess allowing cond reds as a catalyst should be fine. I'm not sure how much lifs heal for but with the delay it shouldn't be any worse than a FS HP. So long as the cond reds aren't eaten or thrown there shouldn't be any problems.