Yes and no
It is ok to use it as long as you do not inhale the alcohol vapor. The best bet is to clean the banger after it has cooled to avoid any of the alcohol from evaporating and you inhaling it.
The alcohol will not crack a quartz banger that is hot, just avoid breathing in any of the alcohol vapors if you use it this way.
We do recommend using a tidy tip after you are finished using your banger or enail. This keeps it clean and you can avoid using alcohol when the banger is hot when you maintain the banger with tidy tip.