Needing for comps is a no-go without asking. I've greeded for many an item my companion could use just to have the last guy need for his companion and saying "but you all greeded, you didn't need them. My comp needs it."
That always annoys me, generally when I start off I say that I'm gearing up X companion and will need only on items for them and will pass on all others. Normally this works fine, if someone says they need the gear for their main and would be polite about it I normally go along with the group anyway, if however they become hostile about I apologise to the non hostile group members and drop group.