Yes, those are cache files from your terminal services sessions. Terminal services sessions are basically bitmapped screen shots, these files are saved to not have to download the same images over and over, just like Internet Explorer saves temporary internet files. Just like Internet Explorer, you may need to go in from time to time and delete them, if the cache gets too big. You can go to options in your remote desktop connection client, and click the experience tab, and uncheck bitmap caching to disable this feature.
In the end, the answer to your question is yes, they are safe to delete.
Matt J.
Please always take the time to backup any and all data before performing any actions suggested for ANY problem, regardless of how minor a change it might seem. Also test the backup to make sure it is intact.