I can barely remember if these sites really offer such instant deposit as I have not played a long time ago on FJ and PD, but on sportsbet, AFAIR, they'll not credit your deposit once it's not confirm yet.
Yeah, most of them require at least 1 network confirmation for bitcoin payments.
If my memory is serving perfectly, I have come across a services which was offering solution for instant deposit through "promo codes". It was working like this: you need to have an account with them and you need to refill your account with any of available coins and then you can generate gambling house specific promo code for your preferred deposit amounts and by using those codes you can get instant deposits to gambling houses' account.
I don't know about that, I'm just referring to the basic steps in order for the money to be credited, different gambling sites have different rules but as of now, I'm not anymore seeing a site that credits a deposit without confirmation. Also, IIRC, Sportsbet does process BTC withdrawal before free of charge, I'm wondering if they are still doing the same now.