As for any other site, I'm sure the admins quite frankly don't give a damn if you refer yourself and get 5% of your loss back, they still have the 95%.
You're missing the point. These sites survive off tiny edges. 1%, 2%. If they give you 5% back when you lose, that's +EV for you. And apparently some give 40% back when you lose!
Actually you're wrong, they lose 5% of the 1%, not 5% of the house edge.
Say im the admin, a user rolls 2.5BTC @ 2x and the number = 49.7, affiliste gives back .1BTC to the user, this would mean i lose 0.025% of my 1% house edge, not 2.5%.
Doesn't necessarily need to be loss from the house edge, but i'm sure you see what i mean.
edit - i had a great post mapped out, sadly, phone crashed (thank you ios8!!)
i'll come back tomorrow with what i was going to say