No, not really true at all. The Sikhs and Malyalees are rather large communities, with large diasporas as well. I think "highhandedness" is too much of a generalisation (?) for such a large and diverse group of people!
You will find that the Sikh and the Malayalis (colloquially, Mallus) were one of the earliest communities to emigrate from India. They've had the time to build a local base in a foriegn country and hence might seem like a difficult group for other Indians to break in to.