Yes, and additionally there are some algorithms that are safe, but to implement require unsafe blocks. I think it's obvious that there are patterns of memory access that are safe, possibly provably so, but not by the compiler at this time.
Since a recommendation for someone to use unsafe could be either a general recommendation with a very broad caveat that quite a bit of additional care and thought, or a fairly benign recommendation to "do X, Y, and Z in this order, and while it requires unsafe, it's no less safe than when we do the same in C/C++", I think it's important to distinguish those, lest someone mistake the former for the latter.
What that boils down to in practice is that stating something requires unsafe is not sufficient by itself as a warning to denote the level of care someone should take. Different people will interpret that statement differently at different times on different topics. There is no need to leave that ambiguity standing when it is easy to clarify. That's all I was trying to express, in response to '"requires unsafe" already implies everything in your comment.'