ToME: the Tales of Maj'Eyal

The learnPool function doesn't check if a talent has sustain_hate as a cost, only hate.

Correct me if I'm wrong, but many purely-sustain talents actually don't make you learn the pool. Is this bad?

There is a specific flag to stop the granting of a pool when it isn't needed. But all other sustained resource costs grant their associated pool.
I think it is mainly to reduce the clutter from escort talents.
As for if it is bad, I'm not sure if you are referring to the use of the flag or the lack of automatic hate pool with sustain_hate talents?