Pretty sure that coinroll is legit and is paying out. Probably just some minor flaws in the system currently, and will be fixed.
Maybe their system has a flaw but bitcointalk is working fine so he can respond here about any issue.
Also, it was just you who is not getting your withdrawal. Personally i have already received one withdrawal
Its just you who got withdrawal,I checked their campaign thread and most of users didn't received any single withdrawal.
I have gambled on their site a few times as well, withdrew a total of 0.6+ coins. I don't think they're scams at all. In fact if they really wanted to scam they wouldn't scam you. Rather they'd either would rig the rolls or simply run away with depositors money.
I have checked their site and in the chatbox you can find many users facing problems with withdrawals.
The whole point of a sig campaign is to get positive exposure.
Are you talking about free exposure? most of users didn't got paid since 3 weeks.