According to my memory from manual (can't find it now), yes. The use of cease to exist airlines like Pan Am is allowed, but not encouraged
Half right -- thanks for pointing me to the manual -- here's the key text:
"As stated in the airline founding / creation page the airlines may not use names that are real world airline names or other trademarked company names, or names that very closely resemble those. The name and logo must be also within good taste and shall not be offensive in any way.
If you are in doubt if an airline or other company with your name exists, a simple Google search is enough to check it. The administration does not expect users to check trademark registries or other sources when deciding their airline name. In other words please use common sense.
Historical airline names may be allowed if it is certain that the name is no longer owned by any other company; it is the responsibility of the user to check this. But generally past airline names (such as Pan Am) are not recommended. Please create your own custom airline instead."
Since the ATA trademarks and logos are still owned by Southwest, I'd suggest Sami disallow the use of it.