Cool! Do you have a picture of the vehicle?
There is no concept of control surfaces or ‘forward flying’ type vehicle in ArduSub right now, but it may be adapted to work. You would need to produce a custom frame configuration as outlined here. This configures the outputs depending on the forces they produce on the vehicle when actuated. ROVs produce roll movement by actuating thrusters, you will do it by actuating control surfaces. This will only work for you when the vehicle is moving forward, but I think it can work while the ArduSub firmware is blind to this detail.
There is some discussion on a similar topic here: