Are they blocking by IP or just DNS? Are you guys typing just domain names, or are you trying the IP addresses too?
Add a line to your HOSTS file and see what happens:
74.113.233.128 vimeo.com www.vimeo.com
Several are claiming that HTTPS still works, which means it's not DNS-level or IP-level. It may be IP+port level, or the only thing that I can really think which is left is deep-packet inspection: a Linux user in India could easily test this with something like:
I got "Access to this site has been blocked as per Court Orders" message when I tried this.
It's not surprising, because a year or so ago Airtel was using deep packet inspection to throttle torrents and file sharing sites. They already have the necessary equipment in place, they can use it when and as they please.