Told by employee of local auto parts store(HD rider)use mobil1 synthetic grease for rear wheel spacers. Is it going to melt and mess up the bearings, just by running into them when the grease heats up? It does say for temps up to 350 F

Doesn't say high temperature though. Should I stop putting the rear wheel back together until I get some high temp silicone grease? Can that be found locally?

What do you mean grease for spacers? If you intent to use grease to stick the outer spacers in place, forget about it. The seals will hold them in place. If you are talking about corrosion prevention, they are stainless steel and don't need it. If you mean lubing the seal lip contact, it's not a problem. You don't need silicone grease for that. Bearings don't get that hot.

I read "HD rider" in the content. Perhaps he can suggest the same oil or lube they use on the muffler bearings.
Probably has in site as to which lanolin keeps the fringe on the handle bar grips supple too.

I have had bearing stick to the axle on some bike so a bit of grease on it is not a bad idea. I use All Purpose White grease or good old Axle grease but it only takes a swipe of it.

I took another look at the rear wheel construction, #11 the retainer gets Super Grease A, the rest are bearings so not needed at this time.

So which of the three in the picture(if any)would be best?, Any of these good for the bearings and dust seal?

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I would use the Mobile 1. I am not sure what you are greasing but I do grease mine when installing wheels. I clean out the dust seal lips. Then I grease the axle well. The grease will slide off the axle as you put it together. Its not needed for friction more for corrosion. I also apply a nice fillet shape of grease around the sealed bearing face and dust seal lips then push the wheel spacer in the seal displacing the grease. Wipe everything up around the spacers if any grease slobbers out I feel this helps keep water out.

The bearings are sealed though and where the spinning wheels friction is occurring. I assume you have checked the bearings for wear while its apart. I just stick a finger in each bearing and pick the wheel up. Then get it rolling and "feel" the bearing rotation for smoothness.

The #11 retainer in the 650 service manual is part #10 in the fiche. I can't really tell what the others are but the Mobil 1 synthetic is fine. Make sure the wider end of the retainer goes toward the sprocket and away from the wheel.

It doesn't matter what grease you use. If it got hot enough to melt the grease, it would also be hot enough to melt the seal and bake the grease inside the bearing into black crust. And the bearings would fail.

The Mobil 1 grease is excellent and can be used for everything. My preference would be Bel-Ray waterproof grease for the added waterproof factor, but use up what you have, first. All standard greases are good to that 350° range, and at that temperature the bearings will lose their tempering and fail. If a bearing is hot enough to take the skin off your finger, even below 350°, you have a big problem, anyway.