For the moment Bitrise webhooks integration with VSTS is only limited for Code Push and Tag Push event.
I’ts very appreciable to have support for Pull Request Created/Updated as well
As you can see in VSTS Service Hooks already have the necessary event for that.
Some organization (like ours) is tied with VSTS and all of our repos are in there. We already have setup our mobile CD/CI in Bitrise and it wont be completed without a PR builds