Gotta say, the moment I'm in a Flashpoint and someone rolls need "for their companion/alt/friend/mother's neighboors cousin", without checking with the rest of the group, they'll probably get kicked. Grouping for quests and heroic missions where they actually use their companions is one thing, but if you roll need for someone you're not using on a Flashpoint when someone else needs it for their actual character, that's just bad form in my opinion.
Remember, your actions have reprecussions. Start ninja'ing, people will recognize it and it'll be harder and harder for you to find a group when you need one.
Oh i agree, however, even if an agreement is made at the start of a PUG run, if you PUG - you always take the risk of someone taking loot they do not need (or for companions). Ill probably pug the early stages and friend people i see as being honest and decent and hopefully find a decent guild to do group content with.
For the times i do PUG, ill endeavor to make sure i am the group leader