Yes, installing Maps Marker Pro on a WordPress MultiSite installation is possible. Just keep in mind, that the license model is domain based, so if you are using subdomains for your multisite installation you need to activate a license per domain. If your subsites are accessible on subdirectories on your main domain though, only the main site has to be activated.
You will find detailled information and a tool tool to propagate your license to your subsites on the license settings page.