I cannot find out if Canon tc's are compatible with 3rd Party EOS lenses anywhere. Of course there's a grundle of info about 3rd party TC's on Canon lenses.
I think it is, at least physically. Looking at the rear of the lens, the rear element is recessed a decent distance into the barrel, so there should be room for the protruding front of the Canon 1.4x TC. The ISO 12233 crops on TDP show it with a 1.4x and 2x TC, and I think Bryan uses only Canon TCs (he didn't have a Kenko, last time I asked, but maybe he has a Tamron one?). But I don't think it will report correctly - the Tamron mount doesn't have the extra contacts that Canon's TC-compatible lenses have.
I had the original (Tamron 70-200 "Macro") for a while and it definitely wasn't compatible with the Canon 1.4x teleconverter that a mate of mine owned (rear element collision). I can't speak for the new one, but I'd want to test the combo out before buying.
