It does highlight implicit conversions by default (they're underlined and have a light blue background colour). I don't think it does anything special w.r.t. macros, but I might be wrong.
As far as I know, they use their own compiler for highlighting type errors in the editor etc. and SBT for the "actual" compilation. The presentation compiler didn't exist when they started Scala support, so they rolled their own solution.
My tests so far are encouraging. I'd like to know their intent with Scala. That plugin seemed to go nowhere for years, and ScalaIDE/Eclipse looked like it would be the only option. But ScalaIDE is still pretty buggy. If they are committed to making Scala support as good as their Java stuff, that would be awesome.
As far as I know, they use their own compiler for highlighting type errors in the editor etc. and SBT for the "actual" compilation. The presentation compiler didn't exist when they started Scala support, so they rolled their own solution.