Are rainproof fittings to connect meter box and weather head to rigid steel conduit required?
Given that the overhead service drop is likely run outdoors, which'd put it in a wet location, 314.15 applies:


  314.15 Damp or Wet Locations. In damp or wet locations, boxes, conduit bodies, and fittings shall be placed or equipped so as to prevent moisture  from accumulating within the box, conduit body, or fitting. Boxes, conduit bodies, and fittings installed in wet locations shall be listed for use in wet locations. Approved drainage openings not larger than 6 mm (1/4 in.) shall be permitted to be installed in the field in boxes or conduit bodies listed for use in damp or wet locations. For installation of listed drain
  fittings, larger openings are permitted to be installed in the field in accordance with manufacturer's instructions.


In general, a fitting labeled "raintight" will be listed for wet location service.  Non-raintight, albeit acceptably corrosionproofed, fittings may or may not be -- check with the manufacturer for their suitability.