Serv-U does not have this functionality, however you could potentially create an Event for when a file is uploaded - fire a batch file that creates a .md5 hashed version of your file and then you could download and compare it in your application.
Probably a late response - for sake of other users who might be on this post with similar question.
SAM has a built in Template called "File Change monitor" which can monitor the file change events including checksum.
See for more details.
However, first we need to monitor the existing of such files using
Here is a short howto Monitoring Files: Is it there? And has it changed?