Glad to hear the welders are being qualified using bend tests. Sounds like the RT is informational only, so it should not be the basis for passing the qualification test. By "RT with a source" are you referring to gamma ray vs. x-ray? I'm not sure what you are referring to here. Below is what ASME IX says about using RT as an alternate to mechanical testing. You can see that RT is not permitted for GMAW short circuiting mode, regardless of the RT technique.
"QW-304 Welders
Except for the special requirements of QW-380, each
welder who welds under the rules of the Code shall have
passed the mechanical and visual examinations prescribed
in QW-302.1 and QW-302.4 respectively. Alternatively,
welders making a groove weld using SMAW, SAW,
GTAW, PAW, and GMAW (except short-circuiting
mode) or a combination of these processes, may be qualified
by radiographic examination, except for P-No. 21
through P-No. 25, P-No. 51 through P-No. 53, and P-No.
61 through P-No. 62 metals. Welders making groove
welds in P-No. 21 through P-No. 25 and P-No. 51 through
P-No. 53 metals with the GTAW process may also be
qualified by radiographic examination. The radiographic
examination shall be in accordance with QW-302.2."