Himanshu Deswal and Kanishka Sharma are two quite known Indian names in the field of teaching CQC, specifically, the system of Pekiti Tirsia Kali. Himanshu Deswal, not so much, Kanishka Sharma is the first Indian to get this system to the country from the Phillipines.
They arent hired for teaching shooting and fieldcraft to SF, they are hired for teaching unarmed combat and combat with other weapons like a knife or stick, and also how to use the primary weapon as an impact weapon in close quarters when shooting isnt possible.
They are the subject matter experts in this particular field. The SF people arent idiots to contract them for teaching them a system if they feel that its not effective.
Kanishka Sharma is personally responsible for setting up the CQC system syllabus at SFTS Nahan, and holds regular sessions there, and presently, there are troops from within the SF who have trained and become instructors in the same at the school.
I know this because I am currently in my sixth year of training under him in PTK at his school in Noida.
And this is nothing unique to India, the same US SOF that you spoke about have contracted Paul Vunak in the past to teach Seal Team Six their CQC system, which is called RAT (Rapid Assault Tactics). Its a combination of easy to learn and really effective techniques in close combat.
Now Paul Vunak doesnt have any combat experience, but he's a world renowned martial artist and the direct descendant of Bruce Lee to Dan Inosanto to him in the system of Jeet Kune Do, which is the system for which Bruce Lee became famous in the world.
And as for PTK, or Kali, its trained by SOF units all around the world for its effectiveness in close quarters combat with weapons and against multiple opponents. These units include ST6, GSG9, GROM etc.