I think that it's very unlikely that there is any vital record that shows anyone other than the senior Obama as the father.
There was no reason for Obama's mother to name anyone else on a birth document — this isn't an area that's noted for innate honesty. Very few birth documents show surprising fathers, even when it is demonstrable that cuckoldry has occurred.
Generally speaking, I would agree. But we need to keep in mind that this is a "Legend". Part of the legend might be called "Out of Africa". Other parts of the legend are known to be inaccurate, maybe that part is too?
But I don't think so. BHO Sr's first wife has been quoted as saying that BHO Jr *sounds* and "acts" like BHO Sr. I tend to think that trying to bring her into forming the "legend" would be a much. Not impossible, but unlikely. It's nice Barry sounds and moves like his Daddy, since he sure doesn't look like him, other than coloration, and then only a rather pale version of BHO Senior's.