Too bad, that is an inconclusive outcome. I'll send a note about this to Cerious just to be safe.
Which version of ThumbsPlus installed this dcraw.exe file? Also, could you state the date/time stamp and the size of the dcraw.exe file?
If someone who reads this is using the same version, maybe he can upload it to VirusTotal as well, to see if his and your file have the same SHA256 fingerprint. If so, your installed copy has not been modified by a trojan or virus.