I don't usually use soap - when I do a rear main, the first thing I do is pour a small parts bin full of clean engine oil and throw the seal it.
You may want to inspect the sealing surface of the crank rather more thoroughly - use a fingernail to feel for a groove. If you can feel it, it will probably cause a leak.
As far as the seal lip, it's going to be fairly flimsy. There's not a lot of pressure behind that seal (and make sure you install it the right way around - the little "V" under the lip should be toward the INSIDE of the engine!) because most of the pressure will bleed off through the forward bearing gap. Granted, there's a little more there than there is behind an axle seal, but it's still not so much (try sealing a power steering box!)
I'm not sure of the utility of lubricating the seal, but I feel better doing it, and it's not caused me any trouble, so I see no reason to stop doing it. The clean oil you used to soak the seal can just be poured right into the engine...
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