Trading free ocs??

^ Echoing above. I personally don't like when my freebies are traded, and on the ownership page it states as much.

so it's really just depends on the designer.

You could always ask the designer if they are okay with it. As others said look at the designers t.o.s. In my opinion freebie to freebie trade would be fair. Maybe you can also draw the freebie before trading it. It might leave a bit of a sour taste if you trade them fast aber getting them or not having drawn them. Just my opinion :)

You have full ownership over the character and can do whatever you want with it regardless of how you got it! If you want to rehome it via trading for art or another character, you're well within your right to.