I don't see how swearing or singing some "gangsta shit" would imply that they're not Christians. I thought you could suck off your dad or snort coke off hookers tits as long as you asked Jesus to forgive you for your sins.
All kidding aside, if someone has faith, be happy they do. Respect them for who they are. Don't bash them for publicly doing what everyone does anyway (and if you're not doing some "bad" stuff... Jesus... live a little!). Swearing, drinking beer, and getting laid don't make a person bad. Aspects of them might, if you take them too far or do them the wrong way. There are exception to every rule.
Anyway... I don't mean to defend I band I've never heard and know nothing about (and assume I would very much dislike), I just hate to see someone get bashed for living. Now prove me wrong, show me they rape or beat up little innocent children, and I'll be happy to go on a rant about them... but for covering a rap tune?