Nalla;
I've already responded to this post in the ASME Forum but will also respond here.
It is "possible" to qualify a welder to both codes simultaneously, as long as all the tests for each code are met. It is also possible to use a 6GR for ASME even though that code doesn't specifically address it, it's something that could be identified in your quality or welding program manual(s).
A special position is one not identified as a "normal" position; your example, in the case of 6GR might be appropriate as might 1GR (rolled).
It is also possible for the Engineer of Record to accept ASME qualifications for AWS works however that is not reciprocal; ASME does not recognise AWS qualifications for ASME works. That said, if you have existing welders who are qualified to AWS or EEMUA-158 and wanted to also deem them qualified to ASME IX, it might be difficult or raise some flags to auditors. For future qualifications, as long as all of the tests for each code are met you could qualify those welders to both codes simultaneously, just be careful all requirements are met.