Eric
Simfactory's key "aliaspattern" expects a regular expression. This allows you to match several host names, which are then all recognized as being the same machine. For example, Blue Waters has
aliaspattern = ^h2ologin[1-4](\.ncsa\.illinois\.edu)?$
which matches four different host names.
There are two other solutions to this. The one I'm usually using (for other reasons, not because of Simfactory) is to explicitly log in to one of the specific login nodes (e.g. ln0003) after logging in to mesabi. This way Simfactory won't be confused.
If you have a home directory file system that is not shared with other machines, then you can also create a file "$HOME/.hostname" with the content "mesabi" (or similar). Such a file will override Simfactory's host name detection. However, the disadvantage is that each user on this machine will then have to create such a file.
-erik