Recently did an on-site pentest at a place that does this (a municipality in the Netherlands). First thing I did was go to https://torproject.org but of course that was blocked. Eventually I found a third party site that offered old versions and via an obfs proxy and bridge node I could get on the Internet uncensored (lots of sites were blocked).

So yup this happens. Is it effective though? No, this took me 15 minutes and I wasn't even an employee with months if not years of time on their hands.