Ooh, this is news that they show up in their own household! I checked and couldn't seem to find them when I did it, so I've been reluctant to sell or give up any pets since. But, my household management has been super clogged and hard to sort through since they did that update and now there's all these ghost households...and households of sims that USED to be ghosts and are now just...idk...there?
edit: all right, I tested this and I don't think it worked. Are you sure they end up in household management? Cause I couldn't find any pets I gave for adoption there.