yes as far as I am aware you can import the user table into your exisitng database.
The reason for doing as I suggest is to be 100% certain that your webserver, mail server settings etc are compatible with USRP. ie sends vaslidation emails, receives validation emails. writes to the database etc etc
Once you know this then it follows that anyhting you do after is where the error is.
So once it's working you can import the table etc and have a play.