I'm not intimately familiar with Hinduism as a religion, but I have a passing awareness of it as potentially an avodah zarah due to its paganism and polytheistic tendencies.
My question is as follows. A Hindu coworker was having a funeral and people were writing "Om Shanti" as a response. Looking up that phrase, I see it both used as a greeting and as a prayer. The belief is apparently around the word "Om" itself having divine capabilities.
Based on all of this, is it assur to use Hindu greetings? Is this considered either (1) praying in the Hindu religion, or alternatively (2) similar to going into a church in the sense of engaging in the Hindu religion?