I was just discussing this with people and I began to wonder if I am right to assumed this. I know many in India and other British colonies did volunteer for the army but is there evidence of people being forced to join as well?
I'm probably too late in answering this, but here:
The short answer is, probably not directly. During British Raj, many kingdoms still had somewhat of an autonomy, provided they complied with all the requests of the appointed British political agent. Many of them had small standing forces and chose to send them into service to get in the good books of the empire. It is entirely possible that political agents may have pressured some of them to send in troops.
For many men, however, especially the ones from certain clans/ castes that prohibited crossing of the ocean (kala pani), there were widespread implications when they returned as they had become social outcasts for breaking a taboo. It is possible that they may have had some inhibitions from participating, but it would seem that they had little choice.