Having a little more background from your other photogrammetry topic, if I understand you and what you’re trying to do with target or control points correctly, then you might not need any ROV GPS-awareness at all.
If the intent is only to produce position-referenced photogrammetry products, you (human) can visit the location above each control point and take surface coordinates there. Depth can be plumbed or measured by flying the ROV. If you’re placing control points manually, then I’d assume you’d already have them on a line and would be visiting each spot already.
Using Agisoft Photoscan as you mentioned in the other thread, you only need a few control points to geo-reference the whole thing. (A location where each picture is taken via the Water Linked system would be nice, but the geo-referencing results in Photoscan would likely only be marginally better.)