I would trust the unicode database here, as I could not find a clear definition of this single character and had to try to extract its meaning from the few compound words it appears in.
I don't know the history of 侑 but it is composed of a left-hand or semantic element meaning "man, human" and a right or phonetic element with the ON or Chinese-derived pronunciation "yuu." "Susumeru" and "tasukeru" are KUN or native Japanese readings. There are several other kanji for "susumeru" and "tasukeru" which are in general use, which this is not. I suspect 侑 was created for, or at least ended up being used in, a specialized purpose (e.g. helping or assisting at a ceremonial or honorific event such as a banquet as opposed to general help or aid). This is speculation on my part, however.