I can at least give some background in case no one else is able to give you more details. I'm much more well read on issue relating to the Chinese and Japanese immigrant communities of the time, but perhaps this will be a start.

The number of South Asians in the US were always low, at least until much more recently. In large part they faces the same sorts of immigration restrictions that East Asians did. In particular you had the Immigration Acts of 1917 and 1924. The 1917 law was also known as the Asiatic Barred Zone Act. The reason being that it restricted immigration from a specific geographic area (and a pretty massive one at that) which included the western half of China all the way to Istanbul, and nearly all of Southeast Asia and the Pacific Islands. The act wasn't solely focused on people from this region, as it also banned immigration from other countries of people in a handful of categories (the application of which could be pretty subjective) such as homosexuals, "imbeciles" and the (English) illiterate. However those from the barred region were more wholly denied.

The 1924 act, known also as the Johnson-Reed Act, banned all immigration from all of Asia. While for South Asians this was redundant with the previous 1917 decision, it reaffirmed the ban and was largely seen as a continuation of the previous law.

It wasn't until the 1940s that these started to let up, and really not until the 1960s that many in South Asia were given more accessible channels toward immigration.

I can't tell you about how people were treated (though I can guess), but at least as far as the numbers and if there were many immigrants from places like India, the answer is that there just weren't that many due to many of the same restrictive attitudes.