I thought that whole thing was some Andalite folklore. Utzum was supposedly the generational gift granted to warriors who were about to die. But, like I said, Tobias had no genetic material inside his body to call upon Elfangor. He had Ax's DNA, and if Ax were going to experience utzum, then he'd call upon his father, not Elfangor.
So no, the general genetic memory thing is not impossible, but the fact that Tobias was greeted by Elfangor is highly implausible considering how it was described.