If you restore, even if from backup, they will not know.
they actually DON'T do any extensive checking. They simply look at it. If they see Cydia or something that can't be achieved without jailbreaking, they know it's jailbroken.
In fact I took my jailbroken 3GS in and they noticed that it was jailbroken and they still replaced my headphones for me after taking a moment to consider it. :P
I've even mailed in my 3G twice in 2008 and 2009, both times jailbroken then restored from backup, and they did not know.
It's nothing to worry about. Unlocking does not 'change' the baseband at all.