The templar has a few skills that are healing vs. pulling aggro or damage. Will the effects of the templar's healing skills ever be of such importance that they eliminate the need for magic items with regeneration effects? Or is it more effective to optimize the templar for his distraction and crowd control potential?
This question is entirely based on your play style and your class. As a tank you are most likely going to want to go with the healing aspects of the Templar if you chose him at all. If you are a ranged character like the Demon Hunter you are certainly going to want them to distract and draw aggro. Also, your Templar's skills will only be as good as his gear. You need to give him gear based on what you're using him for.
You can surely build a more DPS tank with slightly less healing/regen and rely on the Templar a bit. The effectiveness of your follower is only as good as you make it. So yes, with the proper build and play style the Templars heal and regen spells can certainly be a viable option.