Sikhs are the warriors of India - they have been India's guardians and the hardest working and friendliest people. They are revered all across India and referred to as "Sardarji" - which is an honorific meaning "Commander" or "Leader".
India has had many martial communities over its history and up to this day, and to focus only on the Sikhs in this regard is to tell a selective story of the past and present.
In my travels in India I've seen a large number of Indian military personnel drawn from all over the subcontinent. Indeed most of those I saw stationed on the front lines in Kashmir when I visited there just ahead of the Kargil war in 1999 were from southern India.
The interesting consequence of this, was when the Indian Army came in to existence, it had a highly disproportionate share of men from a handful of communities. I know this was true till a few years ago (haven't checked recently), but the Indian Army never released data on the state wise distribution of its personnel as a result.
Another interesting aspect of Indian Army regiments is that they are based on a region or caste for the enlisted members, but the officers can be from any part of the country. So if you're a south Indian officer then you must know hindi and if your parent regiment is say the Gorkhas, they'll teach you Nepali.
Also, there has been a greater emphasis on recruiting from all parts of the country for the enlisted members. Military recruiting has certainly improved and has become much more diverse over the years. The Army doesn't release this data because of political considerations. Politicians are sure to demand quotas if those numbers come out. And letting politicians meddle with the internal systems of a really good institution like the Indian Army is a sure way to gut it.
To clarify recruiting means recruiting of enlisted members. Selection may be the right term for officers.
Not proud of myself for this, but as kids, we'd crack "Sardarji" jokes which are basically the Indian equivalent of blonde jokes.
And it's still the first thing that comes up on Google :/
Sardar in Marathi also means the same thing - "Commander" or "Leader"