Well looking at this https://www.dynatrace.com/support/help/setup-and-... and trying to locate any sign of oneagentutil on the Solaris servers is leading me to believe that it is not supported.
In fact, everything I have found around host groups in terms of docs does not point to Solaris at all.
Unfortunately the docs do not specifically call it out either way that I can find anyway.
While I can not answer for Dynatrace, I would really not expect to see enhancements of any kind around Solaris. It's a dead OS for the most part so I can't exactly blame them. I would not invest in Solaris either at this point.
Although Host Groups are not possible on Solaris, there is the possibility to use DT_CUSTOM_PROP to separate process groups: