Is there any backport of "Grouped filters" available in Views 6.x-3.x branch?
Yes you can do it with Advanced Exposed Forms for views 3 version


  Advanced Exposed Forms (AEF) provides fine grained dynamic data
  filtering by allowing the "joining" of views exposed filters into
  groups. AEF provides AND/OR operators between individual exposed
  filters and between groups of exposed filters. Use AEF to drill down
  from large amounts of data to specific data sets.