There is no known way to get F/A-18 Hornet 2.0 working in SheepShaver. This must be due to some limitation in SheepShaver's programming, because as you pointed out, Hornet 2.0 probably does run in OS 9 on real hardware. In fact, Hornet 2.0 has the "Accelerated for Power Macintosh" badge on its box.
Therefore, you'll have to use Basilisk II, which can run up to Mac OS 8.1 (not 8.6). But then, if you use a recent build of Basilisk II, you'll get an irritating amount of in-flight lag. Only the 2009 build won't cause lag. If you can't run the 2009 build in your native OS, you'll have to run it in a virtual machine running an older version of Mac OS X such as 10.5 through 10.7 (I don't know exactly the last version of Mac OS X that the 2009 build ran on).
In fact you are right I have lag when I run F/A 2.0 on the latest build of BasiliskII. (I guess you tryed several things to run this game !)
Then I tryed the 2009 build, but hopelessly I am on 10.9 : No PowerPC apps allowed
Finaly I tryed to emulate Snow Leopard Server on Parallel Desktop. Fine. Then I tryed to emulate Mac OS7 with BasiliskII IN
this emulation (reminds me the moovie Inception !) But after a quite long time freezing (something like 30s) Something happen : the famous "?" meaning that something does not work.
These 30s makes me wondering : should I try to go farther ? Or this kind of emulation of an emulation is something too deep for a computer ? Does anyone ever succeed in doing such a thing ?