Can the ENH500 in Client Bridge mode connect to an Access Point programmed with a WPA Radius security? If not, are there EnGenius bridges that can do this?

The EnstationAC can do it. All version 2 ENH series and Enstation Series will work. We can check the version number through it's firmware version. The format of the version number is 1.5.x. If the x is any number greater than or equal to 27, it is version 2. Otherwise, it is version 1. Also, if the second digit is less than 5, then it is version 1.