Are wołu and bawołu the only two exmaples of a -u ending in the genetive and accusative singular of an animate masculine noun?
I think it is the only case of both genetive and accusative with a -u ending and probably the only case where a masculine noun has an -u ending in accusative
This is absolutely incorrect. The accusative of
wół is
woła. There is no masculine word in the Polish language that has -u in the Accusative, except foreign borrowings that end in -u and are not declined, ie. Bantu, Hutu, etc.