Hi,
It's difficult to say because nintendo rules are very stricts and only developers that are allowed to deploy for nintendo have access to these details, since Nintendo will give developers a special version of Unity to work for their platform...
I have met nintendo people several times to try and push proper support to their platform and provide quality support for Playmaker, but there policy are beyond insane ( I will stay polite here but insane is the right wording), they are in a bubble of their own and it's very frustrating to witness indeed...
So in short, either you find a nintendo developer that is willing to break the silence, taking the risk to be kicked out of the platform... and let you know if yes or no playerprefs are supported, or you will find out only after you have been approved and welcome in their private developers forums.
Bye,
Jean