Using the engine to hold me on the dock was something taught to me when I took the CYA Keelboat course. I thought it was a pretty nice solution. It just takes a little reverse power to push the stern into the fenders, and that both prevents the boat from going forward, and prevents the stern from moving sideways even in a very strong wind. I use a similar technique to cast off, I put the engine in reverse to hold the boat on the dock, remove the stern and spring lines and have only a bow line (or sometimes no line depending on wind direction) which can be held then cast off by a crew member on the bow. I take it from your generous use of question marks in your comment that you don't approve? :-) Can someone explain the problems/drawbacks with this technique?
I think it is a great technique to use when needed. However, I wouldn't want to do it on a regular basis or rely on it full time. I don't trust bumpers/fenders. Over the 45 years that I've been sailing, I guess I tend to view fenders as something that should only be used to keep a tied up boat from rubbing against another boat, piling, or dock. I never view them as crash stops. Not that I haven't inadvertently used them as such, but I would never count on them.
One of the issues you are facing I think is that you are trying to back into the slip turning to starboard (if I understand your situation properly). The Hunter will tend to back to Port. This may be why you are having to carry enough sternway while you back in to keep the rudder effective. Depending on your situation (you did say you had a very wide fairway) you may find that going forward just past your slip, then reversing and backing to Port may be easier. This is particularly true if you have a lot of room between you and the Hunter next to you. Keep in mind that as you apply forward thrust to stop the boat, your stern will tend to want to move to Starboard. So the least forward thrust you use the better.
I will generally give my crew a mid-ships line to hold as they step off the boat onto the dock. As others have mentioned, this allows some control of the boat without pulling in in the bow or stern prematurely. It is also the line that should be given to a helper on the dock. My guess is that your helpers are getting nervous about your speed and are afraid you will hit the dock too hard. Handing them a mid-ships line with the instructions to just hold it until you stop your sternway, then ask them to pull the boat to the finger should solve the problem of them stopping you too soon or pulling either the bow or stern in.
Etiquette demands that any helper offer help to the skipper before touching anything. If I'm on the dock and another boat is coming in, I'll saunter over to where they are coming in, ask them "would you like a hand?". If they decline, I don't think it is rude at all. Normally, they will respond with something like "Thanks, can you take the midship line" or something of that nature. At that point, I only do what the skipper asks me or what is painfully obvious. I will never cleat their line to the dock unless specifically asked but will hook and hold it until relieved by skipper or crew.
There are exceptions. A dockmate of mine with a new-to-him Catalina-Morgan 440 was coming in to his slip with a huge number of novices on board. He has a very tricky slip to get into, lots of freeboard, and is not yet used to his newer boat. I ended up taking both a bow and stern line from his crew and helped pull the boat to the finger. However, the entire time the skipper and I were making eye contact and each knew what the other was thinking. I was following his lead, never the other way around.
So, to answer your initial question:
1) Accept or decline help as you wish.
2) If you accept help, give specific instructions to the helpers.
My wife tells me I'm terrible at giving clear, specific, instructions. I just the think the rest of the world is filled with idiots.