Is it possible to use baseband at 4.10.01 on iOS 5.0.1?
How, considering that redsnow 0.9.9b8 is does not recognise 5.0.1 ipsw?
Is it safe to upgrade iOS wirelessly or it will upgrade the baseband too?
Baseband mismatching is not something you should jump into haphazardly. Apple tunes the baseband for the specific build of iOS. Running mismatched is not advised and you may experience problems that range from dropped calls to excessive power consumption. All of which are almost impossible to accurately diagnose.
Redsn0w doesn't provide baseband preservation. You'll need to look into PwnageTool to preserve your baseband.
Upgrading using the OTA update will update the baseband along with the OS. When you say "safe," I'm assuming you are talking about baseband preservation (see above), so no, it wouldn't be "safe" for unlockers.
But considering there's no actual unlock for baseband 4.10.01 on the iPhone 4 (GMS), it really doesn't matter in this case. The last unlock available for the iPhone 4 (GSM) was for baseband 01.59.00, which appeared alongside iOS 4.0 - 4.0.2. And since you can't downgrade your baseband, you needn't concern yourself with the preservation.
The Gevy unlock SIM card works with bb 4.10.01.
It is very important for Gevy users to preserve the baseband at 4.10.01.