Long exposure astro cameras with higher dynamic range are certainly better for photometry but I played around with 8 bit camera photometry a few years back and found it was possible to do high(ish) precision photometry with 8 bit cameras (even exoplanets, just) provided you sum many frames to get the counts. eg
http://www.threehillsobservatory.co.uk/astro/Photometry_GO_Com.htm
http://www.threehillsobservatory.co.uk/astro/TrES_1.htm
One thing to watch though with these cameras is that the gamma is set to 1 so the response is linear.
Cheers
Robin