I have a working install with GF 1.5.rc2.1 and the User Registration Add-On version 1.0.beta1. Now when I install the newer Registration add on (1.0.beta2), it says it can not be activated because "Gravity Forms 1.5.beta3 is required."
I noticed that on the download page, GF 1.5.rc2.2 is available, but no 1.5.beta3. As a matter of fact, after updating GF to rc2.2, it still says it runs rc2.1; it looks like the version number is not edited in gravityforms.php.
I realize this is all beta-using-related, but all in all it's quite confusing, so I thought I'd let you know.