No it's not. The are still technically "sparse", but will always eventually grow to the maximum size of the vdisk and never shrink, won't be trimmed etc (ie: as you add files to the VM, the image will grow, but when you delete files it won't shrink. You eventually (shortly) get to a point where the vdisk is the maximum size and stays there forever
To enable this, you need to do (and as a bonus, write performance will also increase)