Unrevoked ONLY s-off's CDMA desires so if you are GSM (uses SIM card) this is not the case.
only AlphaRev 1.8
S-offs and yes it can be risky.
You dont need S-off to flash roms though.
Rom manager uses a fake flash clockworkmod, but you have clockworkmod already flashed using unrevoked.
Rom manager is a work around from before we had the ability to root with unrevoked so we could use clockwork, but now unrevoked does this, no need for rom manager.