Does plugin use standard wp login/registration

I’m not sure what you mean, exactly, by ‘create a separate user’. The plug-in doesn’t require any log-in, and doesn’t provide a means for users to log-in or out. By default, all it provides is a link to log-in, which can be filtered if you want the link to point somewhere other than the default log-in form.

Thanks Joe,
I just want to insure user is logged in to purchase and isn’t forced to create a different account upon checkout.

No, no requirement to create a new account.