Unless a virtual hard disk is actually using a RAW Disk then a virtual hard disk is just a file on the Host's Filesystem and therefore any disk utility run inside a Guest OS I'd have to say is not technically or actually preforming the test directly on the Host's physical hard disk in the same capacity as if run from the Host itself. That said however... obviously if there is a bad sector on the physical hard disk within the bounds of where the virtual hard disk file(s) resides then there will be issues while reading the virtual hard disk from within the Guest OS. So in essence assumingly the end goal is still achieved. However if you suspect the Host's physical hard disk has bad sectors then you should test it directly using the manufactures diagnostic utility, if available, or other industry standard testing utility. A simple test could be if the .vmdk file(s) that comprise the virtual hard disk cannot be successfully copied to another location this can be an indicator of bad sectors and or a failing HDD (or may be a corrupted filesystem on the Host).
