but I would not have thought that you would damage transfer case in that scenario. My understanding is that the transfer case is engaged when in 4WD and all that does is split the movement of the running gear between the front and back axles/diffs. The hubs are engaged at the front so that the front wheels then get the benefit of the moving front diff/axles. So if there not engaged, then the front wheels are not pulling as far as I can tell - like I said, Im no mechanic, don't quote me on that.     

I wouldn’t think you can damage it this way. And if it’s a concrete ramp, I wouldn’t lock them anyway. The pressure on both front wheels is the same, so they should turn together, unless one side slips and the other doesn’t. Beach launch is a different story. But again, I don’t think you can damage something. You might not get the boat out if you don’t lock them. Well, that’s my theory.

the only way to damage it would be to lock your hubs in and start doing 3 point turns on bitumen.  Even if you want to lock your hubs in as long as you go in a straight line just to get up out of the water and put it back into 2wd you wont do any damage

Wont do any damage. this is one case where manual hubs rule.

It shouldn't be a problem mate, all your doing by putting it low 4 but not locking the hubs in is changing the gear ratio. All the front running gear eg the diff centre, front tailshaft and axles will be driven but just not connected to the front wheels because the hubs aren't locked. I do it all the time when reversing the boat up my driveway, makes life easy.

It shouldn't be a problem.

Just be aware that you are producing huge amounts of torque in low range and channeling it through one diff. Just dont give it a gut full of throttleand dump the clutch or you could do damage to the drive train