I do both and agree with everything that has been said, however I will say I see massive benefits in flexibility, movement and core strength from Jitsu into mountaineering.
I am following an extended 24 week expedition programme, and I will say my cardio and Strength in BJJ has seen massive benefits.
Jitsu is the icing on the cake for training, and like said above just dont let it replace your Z1-Z2 endurance workouts.