Is it absolutly necessary to lock a surface before rendering? Are there any other ways to go about doing it?

Lock() is required before directly accessing the bits in the surface. Sometimes you can lock, unlock, but still use the pointer, but this is very device/OS dependent, and it can cause a crash on different computers.

You can Blt() and Draw*Primitive*() without holding a lock, in fact these operations require that no lock is held.