Yes, which is why Signal is doing a disservice by telling people to announce their proxies on Twitter. The expats should just tell their friends and family, and tell them to pass the word on only to people they trust.
But this doesn't stop them from doing that. If you have an expat friend or family member with a proxy, use theirs, if not, check the latest tweet with the hashtag and use that.
That's not to say it's a free society or that censorship doesn't exist there, just that it's not the sort of regime that is particularly good at it.
If I had to guess, Iranian expats would be a likely set of people to start up proxy servers for their family and friends back home.