I believe HideParticleEmitter() removes it from the rendering queue, but it won't remove it from memory.
Be careful not to overload your system with too many emitters.
I guess its up to you to decide if they should be hidden or created as you go. Maybe the best way is to keep the most used ones hidden.
For easy access and no load time. Then the rarely used ones could just be recreated.
Of course this would be if you had many emitters. If you only have a couple I'd just keep them all hidden.