Is the NOLOCK hint completely safe to use on a table that's guaranteed not to change?
If I have a table where the data is guaranteed to never change, is it completely safe to add the NOLOCK hint to my SELECT queries against that table?


In practice, yes (although not documented as such), but also useless.  If your data never changes, then using dirty reads won't cause any observable behavior or material performance difference.


  If I have a table where some of the rows will be updated, but I'm only selecting rows that are guaranteed not to change, is this also a completely safe scenario to use the NOLOCK hint?


No.  Absolutely not.  The query plan to read the target rows may read changing data structures without proper concurrency controls.  So you are back to hoping that your queries don't return bizarre, incorrect results or simply fail.