Yes, it can be used with or without the supplied mount. I suspect that's included in case you wanted to run it on something like a small rifle that uses picatinny rails.
Without the mount, it's designed to mount directly inside milled RMR cuts. I don't know if you can use adapter plates like those suppled with Glock MOS systems to mount it on non-RMR slides. The Holosun 510C is quite popular with the AR15 crowd due to it's success in competing with the Eotech's for half the price. Alabama Shooter on youtube is known for his rugged testing of optics, and he shot one with a shotgun, reinstalled on his AR and it kept functioning perfectly lol. That pretty much blew the market open for Holosun. I have a 510C on my 7" AR9 build and it's very nice for the $215 I paid for it.