Well, camcreating artillery shells works in MP, it's just not desirable.
And if you use camcreate correctly, you can get MP effects that otherwise would not be obtainable.
In most cases where a shell is camcreated, you can go ahead and createvehicle. In fact, you could dot hat to my artillery suite available int he tutorial section (just go to multifuzeburst and shottosplash and replace the camcreates with createvehicles), although the ICM would lag.
Actually, the reason why the ICM would lag is because there you've gota case where a camcreate is a better choice. Creating hundreds of projectiles nad transmitting them to all clients in the span ofa second is a recipe for MP disaster.
If oyu look at what we did with the AP mines (CoC_mines), you'll see that we used camcreate for the projectiles, and with remote spoofing (=camcreating dummy bullets for the sound and visual effects on non-local machines).
That camcreate works that way is desirable. CreateVehicle wasn't extended to shells until 1.85, and that's a goodt hing too. Know your tools.