ASME IX qualifies for pressure vessels, atmospheric tanks and piping. AWS D1 qualifies for structural steel. Welding ships is quite a different thing. That's why shipyards require qualification according to a shipbuilding certification, such as Lloyds or ABS (American Bureau of Shipping)
Giovanni S. Crisi
Sao Paulo - Brazil
In my experience, the answer depends on the classification of the vessel. If it is a Mobile Offshore Drilling Unit you should expect to have to retest in the presence of a Lloyds Surveyor unless you have a certificate issued within three years (backed up by certified activity every six months) from an IACS (International Association of Classification Societies) member.
If it is a vessel with less stringent service, the assigned surveyor may accept other credentials. Most likely they will not be accepted unless they were issued by one of the IACS members, such as ABS. Furthermore, there is generally a time limit on Lloyds certificates (typically three years, after which retesting is required regardless of activity history).
Charles
PS - Structural Welding in accordance with Section IX requires a 2G plate in addition to 3G and 4G (which are all that AWS D1.1 requires).