Is it possible to use Nordic's UART Serial Port Service when a BL65x module is configured for UART Bridge Mode rather than using Laird's Virtual Serial Port Service?

Yes, if config key 112 set to 1, via the AT+CFG 112 command then the service UUIDs for the UART serial port service is as per Nordic’s implementation. Any other value will use the service UUIDs for Laird’s custom service - vSP (Virtual Serial Port).

Please reference the Virtual Serial Port Service Managed section in the smartBASIC Extensions User Guide of the BL65x module you are working with for additional information.