I recently tested this on my Mac (Lion - 10.7.3) and it worked fine...
Here's what I did...
I created a standard CIFS volume and share on my Filer (Volume - RF_TEST, Share - RFTEST) - I used Systems Manager to create my volume. Next I mounted the share over SMB on my Mac (passing my filer domain credentials in the process):
I write files into the directory:

After about 30 seconds – Spotlight has the files indexed and results are shown (not sure if the number of files has a relation to the amount of time the index is shown):

Showing in Finder:

Full info to show it's on the Share:
