Can I use the same database for WP and SMF?

I installed a forum alongside WordPress and I was wondering if I could use the same database between the two.

Basically what I want to happen is when somebody signs up on my Forum or WordPress, that their account details can be carried over across the two platforms. So, if Joe signs up on WordPress, an account (named Joe) is created for him on my forum with the same username and password.

Is this possible? I have no experience with SQL databases.
And, if it is possible, could I just… merge the data between the two? Because I assume I’ll lose all data if I were to do this right now.