Return active pool members from log local0. in an irule?

Is it possible to list the active pool members for a specific pool using the log local0. logging command in an irule?

Yes.

Start with looking at: Pool Member Status HTML5 Page

Instead of creating HTML content, just log to local0.

e.g.

when HTTP_REQUEST {
    set thispool "my_http_pool"
    foreach { pmem } [members -list $thispool] {
      log local0. "$thispool - [getfield $pmem " " 1] [LB::status pool $thispool member [getfield $pmem " " 1] [getfield $pmem " " 2]]"
    }
}

I hope this helps.