Advisors and liaisons are pretty common fare for Vietnam. Advising the ARVN airborne division was a big deal, SF raised Montagnard troops in the Central Highlands/Laotian border, there were other ethnic minority (Hmong, Nung, Khmer, etc) forces similarly raised by SF, the Marines were working with CIDG's to pump up regional/local security in the I Corps region and the SEALs, later on, were working with the LDNN's.

That doesn't even encompass SOG operations in Cambodia and Laos where the on-the-ground recon was conducted by mixed teams in places where they weren't supposed to be or the Phoenix Program, which had advisors directing Vietnamese 'mercenaries' to eliminate VC infiltration of the RVN government.

There was a similar degree of fluidity between where the advising stops and the operational control starts in the VNAF as well.

Here's a thought in determining things; work out the region of Vietnam and the time period. The border with the North is a very different animal than the Mekong Delta, which is different from the Central Highlands and so forth. From there, we have a much better idea of what the force mix might look like, since ROK and ANZAC forces, for example, operated in two very different spheres.