i havent really had this problem (i once got grouped with 3! sith sorcs on group finder and simply passed on all the light armor) i will likely pass it unless, say, it is an upgrade leaps and bounds above something on vette, quinn, or jaesa, in which case i simply greed it, because really, i can always search for an upgrade for companion gear on the gtn.
but if you need on something class locked, unless you are that class, i do not think you should get that item.
simply remove the "need" button on items that are class locked unless you are that class.
I think it's the "nice" thing to do pass/greed on stuff your character doesn't need. I do that, but I also can see the other side. What if that player is doing that HM/OP with the sole purpuse of gearing up a companion, for example ?
If you see it as "your character" vs. "someone else's companion" yeah, ofc the former is more important.
But that's not the only way to see it. You could just look at it as people's time and effort. Everybody is the same. They all are behind their computers doing whatever is needed to get through the instance. No one can claim they have more right than the next one for whatever stuff is dropped.
A slightly different example. I did a raid a while back. One of my guildies decided to gear up a bit one of his alts. But when the time came, oops.... no, the op leader told him that he couldn't roll on stuff because people's mains had priority. I understand the reasoning behind it, but that sucked regardless. He worked just as hard as everybody else and got shafted because some sort of arbitrary reason.
How loot is handled is a delicate matter and ideally everything should be talked to and agreed on, but can be hard to do in a pug. You don't truly know what are other people's motives.