Time Machine is a wonderful backup utility for many types of files. Unfortunately virtual machines are not a good match for it. Time Machine does not create reliable backups for your virtual machines. The explanation is a bit too long to put here. For the details on the reason why, please read "Why not to use Time Machine to backup your Virtual Machines".
The good news is that Vimalin has been designed to make reliable backups of your Virtual Machines. It does so by working together with VMware Fusion and its automation facilities so that proper backups can be made from your VM even when it is running.