The identification of Brahmins as "rig vedic" has nothing to do with their identity. They just belong to a school that taught them Rig veda and its practices for yagna.
There are many mantra's in the rig veda that is chanted in isolation and not as part of the entire rig vedic chant. For example the " Maha Mrityunjaya Mantra" (of shiva) is part of the rig veda, but even Buddhist chant them.
So does thousands of others hindus.
Here is a video of Buddhists chanting the Tryambakam Mantra (Maha Mrityunjaya Mantra from the Rg veda). So are you going to claim that the Buddhist follow the Rig Veda ?