Well I don't use Spyware Doctor (SD), so I don't know what the purpose of that Temp folder is within the avdb folder. I can't even find any useful information on the .vbt file type to be of any help
It may be that for scans it unpacks it database to try and speed scans, or possibly like avast it uses the _avast4_ to unpack archives so their contents can be scanned. So it could be possible that something that SD opens to be scanned is first hooked by avast and scanned. After running an SD scan is that temp folder emptied of .vbt files (like avast empties the _avast4_ folder after a scan) ?
So there is more to this than first meets the eye and you need to seek confirmation from the SD support forum as to what this temp folder and the .vbt files are/do.
So contrary to my advice on the exclusion of the *.vbt until we know what the purpose of these files are it could be leaving a hole in security. Whilst it would be possible for a virus to get in there it would also have to have a .vbt file extension/type to also be excluded, so it is a risk but not I would say a high risk.