What a load of crap. from where this "brahmin sect" came from? Brahimns are said to be Hindus and have nothing to do with Family of Prophet Muhammad (PBUH).
This conspiracy theory proves two things
1. Brahmins either are NOT Hindus and outsiders who became Hindus to rule the real Hindus in Sub-continent. Therfore the Dravidians are right when they disown "Aryan" theory.
2. OR, The Indian Hindus are trying to infiltrate Islam through such concocted stories.
You are barking up the wrong tree (that was a metaphor and not intended to be taken literally; my assessment of your posts and your general point of view did not intrude into this).
There was a very strong tradition of mercenary warfare among people throughout north India, among the Mohiyals or Hussaini Brahmins as reported here, but also among the people of Bihar and eastern UP in general. This tradition has been traced back at least to the first five centuries AD. References of the researchers who have looked into this tradition of 'naukri' are available.
The Hussaini Brahmin and Mohiyal traditions are known widely, and have been known for centuries now. It is unlikely that holding this belief through the difficult years of domination by one set of armed adventurers after another, all professing the religion and faith in the pillars of that religion, would be due to some ulterior motive.
Your first point is meaningless; the tradition of martial service with others did not involve a change of religion. Some of the most effective, dangerous and bloodthirsty Afghan and Persian and Turkish invaders of the first millennium and immediately after had regular formations of Indian troops, who were Hindu, and remained Hindu, and had their own subordinate leadership, which itself was under the close supervision of the Sultan's picked men. An occasional foray into history is a good corrective for the sensationalist journalists point of view that point 1 displays.
Your second point is, to put it mildly, Islamocentric to a laughable extent. People have better things to do than to 'infiltrate' Islam, for no apparent purpose.