I'm growing disenchanted with Prowl, though--the speed reduction makes it hard for the Ninja Jungle Cat to keep up with me when I'm running.
After retraining the Ninja Jungle Cat, I determined that the effects of Prowl and Dash do stack--but the combined effect is still slower to enter combat than unmodified speed.
And the Prowl only gets a bonus to the first attack it makes. So unless I'm wanting to use the scouting ability, I'm not sure how useful Prowl is.
So I'm still waffling about my preferred set of four active skills for a pet. Growl is certainly on the list. I'd follow that up with an attack power (probably Claw for a cat, because I don't see Humar using Bite quite as much), and probably Dash. That leaves one slot, for which the candidates are Cower, Prowl, and Bite. Of these, I've just recorded my frustrations with Prowl; I usually leave Cower turned off; and Humar usually uses Bite once and then focuses on Growl.