Buxfer are from India. I think they were on student visas initially but then switched to work visas.
YC's philosophy (from talking to everyone involved) seems to be if you good enough regardless of where you are apply. Visa complications are obviously a pain but if your get in you get in.
But, I understand getting a work visa can be challenging and time-consuming. Temporary for the 3 months might not be as big of a problem...Auctomatic came from England for YC and only stayed 90 days (with plans to return ASAP). Maybe Kulveer or Harj will chime in with what they had to go through to make it happen.