Exporting results from one plugin into another plugin is definitely possible. You typically have two steps:
1) Export the data from a producer plugin
a) using Tokens
b) using API methods of the plugin
2) Import the data (or reformat and aggregate it) into a consumer plugin
For step 1 I can say this works for the warnings plugin, it can export the results of CppCheck either into tokens or into objects (that you can process using your pipeline).
I have no idea if the slack plugin is capable of doing step 2 though, but I would assume that it works in that way...