You can safely use the singing sword with Hep ancestor (just verified it with a quick Ziggurat Sprint)
Probably best to stick with the weapon you have as your primary one.
That said, I could see the singing sword being useful late game. Bow weilders of Hep don’t have many options for dealing with large crowds, so having the singing sword as an alternate weapon might be a good way to overcome that weakness (and there’s plenty of xp and gold in extended.)