Well that doesn't sound encouraging, so why not go on dweeb-ing?
OK, when you had all your polygon groups right, and went into the fitting room and click, name, clickity click you're outa there,
you've got your rigging.
That's the slick part.
But, as I feared, if any geometry is not very near the horse's geometry the weight maps are blank or meaningless.
Only it's not as monstrous as it seems.
If you save the new mane figure, then put away the horse and load up the mane figure again, you can use the Joint Editor.
Well you just go to 'Windows' I think and open the Joint Editor window, and then go through each body part, and each coordinate, like bend, twist, side, or Xrot, Yrot, Zrot, and you see there is a section which shows you have a weight map, and click on delete for each one
You will be prompted to verify, click OK every time and alas the weight maps will all be gone.
So then you are left with the default include, exclude, angle functions, which, unfortunately won't be just right because the rigging is a bit unconventional.
So you could go through tweeking those angles, OR, you could use the capsule approach to setting the smoothing/falloff and the mane can come out working pretty nice.
Then if you want you can have those capsule zones automatically converted to weight maps if you want to do some finicky editing.
Only you say NO NO NO please, not that! So the capsule things will probably be OK.
Now, you're probably saying 'No wonder there's no seahorse for Harry, what a bother' and you would probably be right.
And you could always say 'Hey, I did a fantastic job in DS, if these crazy poser nuts want it, they can convert it themselves'
which might not be real nice, but not unreasonable.
Plus, there's other ways. Take a look at how the HiveWire Mane is done.
It has all the Harry rigging needed and no geometry to match, but all it's own geometry parented to the base geometry.
Now there's a monster of a task.