Let me define the terms:
Not Compatible: Android apps are "not compatible" with the iPhone. They are never going to work together.
Not Supported: Apple does "not support" Cydia on the iPhone. They do work together, but Apple is not going to help you with it.
With the Pebble team saying that WP8 is "not supported", reading between the lines, they are saying that the Pebble and WP8 will work together. They are just not going to help you with it.
So my questions are: How well can I reasonably expect them to work together? The lowest hanging fruit is pairing. Will they pair? The next is caller id. Will that work?