I have successfully paired my X51v with two different BT USB dongles using BlueSoleil software on two separate computers.
One thing I'd suggest for you is to make sure ActiveSync both on the host computer and on the Axim is set to use Bluetooth in the options. The option must be set on both sides in ActiveSync.
It takes a little back-and-forth toying with BT settings on each side but it will work with your configuration.
See this thread for some more pointers...
Axim X51v Bluetooth Sync, File Transfer, and Internet Browsing Guide