Can the U1 locator be directly attached to an ROV/AUV?

Yes, it can be directly mounted to a vehicle using any practical means.

When mounting it, make sure the locator will be in direct line of sight with the topside antenna/receivers.

The U1 comes by default with mounting brackets in stainless steel. We also offer a couple other mounting brackets:

https://store.waterlinked.com/product/locator-u1-gopro-bracket/

https://store.waterlinked.com/product/locator-u1-blueye-bracket/