Dropped a support request at Sena, will keep you posted.
Ok, heres the answer from Sena:
Chris Woodyard, Sep 06 16:51 (PDT):
I cannot say that there are any known problems between those two products as it is difficult to test every phone on the market. However, I was able to find this while researching and I think that it applies to your issue. how do you set the "default launcher" for HTC1s. The 5th post details how a user was able to set their wanted app to launch when a specific action was performed. The same thing could apply to setting the voice dialer on the HTC One to be launched when the phone button on the SMH5 is pressed.
Technical Support Engineer
Sena Technologies Inc.