Is there a list of validated Ada compilers?
Yes, indeed, there is. The latest list can be retrieved by anonymous FTP. For Ada 83, it is in ftp://sw-eng.falls-church.va.us/public/AdaIC/compilers/83val/83vcl.txt (if the list is updated during the month, the previous one is replaced). And there is also a (non-empty!) list of validated Ada 95 compilers at ftp://sw-eng.falls-church.va.us/public/AdaIC/compilers/95val/95vcl.