Whatever is best for inbound leads team to analyze data on a newly acquired lead. I've currently just added them as hidden fields to the form. As long as they can get cleanly maintain attribution for inbounds out of that I'm satisfied, but if there's a better way let me know.
Hey, I know it's been a while since you raised this issue, I was wandering if you came up with a solution? I'm currently facing the same problem. Trying to pass UTM params using the submit form API for a non HS form. Can't seem to find anything to help me understand how to pass those fields.