Pulling in variables about the group works.
e.g.
<B>Group:</B> ${Name}<BR>
I'd like to be able to include a custom property but I don't know how to reference it...
FYI SolarWinds support have said that they would have expected group custom properties to be referenced in the same way as node custom properties which doesn't work and that this is a bug.
They will hopefully fix it in a future release.