Yes, when you don't snapshot the virtual memory, the snapshot is a crash consistent backup of the vm. Therefor, if I want a clean snapshot, I will shutdown a vm before taking a snapshot. Crash consistent is typically ok, unless you are running apps that keep things in memory, like sql db's, exchange, and things of that sort. For those, it is cleaner to shutdown the vm if you can. Otherwise, if you're not using volume shadow service that's part of vmware tools now, then you risk crashing your db during the snapshot's quiescing process.
-KjB
vExpert/VCP/VCAP
vmwise.com / @vmwise
-KjB