Error = find: -exec: no terminating ";" or "+"

Just terminate the find command with \;, making sure to include the space before the \;.

find /Volumes/NEXSAN/Engine\ Folders/Input/DTO_Proxy/* -type f -mtime +7 -exec mv -v {} /Volumes/NEXSAN/.2BeDeleted4realz/ \;

If you want to correct the find command that you had, it should look like this:

find . -name '*.xml' -exec SetFile -t TEXT {} \;

The *.xml needs to be quoted so it's passed as a parameter to find instead of expanded by the shell. The ; also needs to be escaped so it's passed as part of the parameter to find and not interpreted by the shell.

Keep in mind this will only work for files within the current directory (and subdirectories) and for any new files created, you would need to run the command again.