Since then I have been in Vahlok's tomb, Nchardak, and Fort Frostmoth and at each one of them at least one Riekling has shown up to assist me. Once it was at least three of them, they only seem to show up when I get into combat and then they follow me until I leave the dungeon.
I have none of them as active pets as far as I know. And as surprisingly un-annoying and helpful they are I would never have sided with them if even limited forced companionship was the reward.