Can I use the professional edition and the standard edition of SourceAnywhere for VSS simultaneously?

Theoretically, yes. However, the professional edition and the standard edition are not compatible. You have to install both the servers of the two editions and the specific client can only access its own server.

Since the Professional edition and the Standard edition are using the same Service name: Dynamsoft SourceAnywhere for VSS (version number), the service of these two editions cannot be started simultaneously. If you install these two servers on the same machine, only the latter one can work, which means if you want to keep these two editions, you need to install and maintain 2 servers.