Yes, I believe your idea would work just fine and I have gone down the exact same line of thinking you have, even to the point of originally selecting the same radio. Here are my thoughts on the subject:
The adage that if you fall overboard, you are dead is there because of many years experience and still holds true. I do believe that technology and innovative ideas could start to change that.
I believe the main problem as to why the MOB is likely to die is because they are difficult to find, and find quickly. Recovery is another issue, that could be addressed with readily available gear, but honestly I haven't read too many accounts of people drowning beside the boat. They are usually never found, or drowned when found (ie it took too long to find them).
I think that the problem of trying to locate the MOB has been backwards for some time. A MOB pole is nice, but it takes a race crew to have the spare people to launch it. Often the MOB can't swim to it either. Dye markers, strobes, reflective tape etc, make the needle in the haystack a slightly larger needle. I think this is the wrong approach the MOB will always be low in the water and usually hidden by swell, and thus impossible to find. I've been on a boat offshore in Hawaii looking for a 5'diameter yellow buoy before and we were darn near on top of it before we saw it. Even though it was big and yellow and had a flashing yellow light, it was only 5' tall and we were in 3' chop mixed with swells.
The MOB on the other hand can see a 30, or 50 foot mast much easier. And if the MOB can see the mast, and has a way to talk to the boat, he can steer the boat to him.
For those that don't think that the VHF in the water has much range, consider this. VHF is line of sight right? So if you can see the mast (which is presumably where the receiving antenna is) you can talk to the boat. Or put another way, how far away have you been able to spot another boat's mast? 5 miles? 10? 15 miles? If you can see the mast, you can talk to it.
The formulas for how far a mast can transmit or receive are easy to find on the web. A 50ft mast has an approximate transmit/receive distance of 10 miles to another antenna which is 0 feet above neutral, and a 30ft mast is just over 7 miles. As for power, have any of you ever tried using the "low power" button on your VHF? It transmits at 5 watts (which is what most handhelds are) and it transmits really far. Try it some time.
I don't think there is any advantage to the HAM radio that you've picked out. As you mentioned, the protocol would be to have the mother-ship monitor 16 with the volume tuned up. So all you need is a radio that transmits on 16, which a handheld VHF can do. As mentioned by another poster, a handheld WITH DSC will be able to not only communicate with the mother-ship, it will be able to, at the push of a button, transmit your GPS coordinates to the mother-ship. Have you ever been aboard a boat that has a DSC radio and has received a DSC distress signal? It sounds like a smoke alarm!
I wouldn't think that the HAM would have any benefit above and beyond a marina VHF. You won't last long enough to have SAR come and get you even if you could contact them on land, and I doubt you could. If nobody is within your 10mile VHF range, then nobody is there to save you.
If the plan goes like it should I could imagine a scenario where you fall overboard and the other crew is sleeping, but the mother-ship's DSC capable VHF is on. You push the DSC button and the klaxons wake up the off watch. The off watch enables the mob function of the radio and an arrow points to your location. The off watch steers by the arrow to your coordinates.
Meanwhile, or once the boat is turned around and close to your position, you can see their mast and are able to communicate to the boat. "400 yards off your port bow! Turn a little. OK now I can see both red and green at the top of the mast so you're headed right for me. Hurry up I see a dorsal fin! Okay you're almost at me, do you see my strobe yet?"
In a different scenario you fall overboard and the off watch is asleep. You activate your strobe, blow your whistle, and activate your PLB. The off watch doesn't hear the whistle and the location of your drowning 40 minutes later is recorded by the SAR authorities a continent away.
I think it's an eminently practical idea and as a side benefit the radio you buy also functions as, well, a raido. The PLB doesn't do much else.
I just carry a remote for the auto-pilot.
Now there's an interesting idea...... Are you serious or kidding?