The problem is, once in Keynote PPT themes consist of TWO master slides. Kinda skimpy when you compare it to sometimes up 30-40 master slides in some Keynote themes (though Apple's have less, usually 13-20).
Create a PPT file, and use a Title slide and a regular slide (title and bullets, etc). Save it and open it in Keynote. You should see two masters.
If you want to save this out as a theme read this tutorial I made a while back:
http://www.keynoteuser.com/tips/savingtheme.html
the save location is actually old, but it WILL still work. The new path though, is >application support>iWork>Keynote
notice the addition of the iWork folder in the path. Either location will work, but the second one is the preferred location.
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slide types in PPT are set by Microsoft, they don't exist in any template. Templates consist of a title slide, and an "everything else" slide, which usually looks like a title and bullet slide, but gets applied to all the other "types" you get to choose from in PPT.
Making a file filled with different type slides will get you the same thing as using two slides: a keynote file that contains 2 masters. You would then duplicate the masters and change them to your liking.
The only other way to do what you're talking about is to turn on the "multiple master" support in PPT and copy and paste every type of template into one slide..so instead of a bunch of slides based on the same template, you have a bunch of slides, and every 2 of them would be based on a different template.