In the manual I found for this transceiver the note about BTL amp output is for the connector in the back but not for the front jack. The connector pinout provides separate pins for SP+ (4) and SP- (7) which leaves room for possibility of BTL on the front as well.
From previous report it appears that the cable works as above here. Still, recommendation would be to not initially ground pin 7 and try operating with just pin 4 connected. There is no danger to Digirig in any scenario.
Similar cable and BTL also discussed here: Cable for Anytone AT-778UV