Yeah, I've gotten it to work, but it does require some minor manual intervention.
The plugin(s) are designed to work by just putting a link in the dropins folder of your Eclipse installation. After the installer completes, you should have something like a "/Applications/Adobe Flash Builder Plug-in Beta 2" folder. From there, look in "/eclipse-host-distro/dropins". The link you need is in there. Copy that link into the dropins folder of your STS install. It should get picked up the next time you start STS.
Staff Engineer, Web Products Team