Pitting by itself does not necessarily make a barrel inaccurate. However, it does mean that the barrel will foul much faster and, once the barrel is fouled, accuracy will decrease.
It’s safe to shoot once you’ve scrubbed the rust out. Otherwise, the rust actually decreases the bore diameter a bit and can jack up pressures (though your barrel doesn’t really sound that bad).
While normally a bad idea, running a stainless steel bore brush through this barrel a few times would be a good way of getting the rust out. Depending on how bad the rust is, you may need to pull the brush through the barrel rather than trying to push it through.
Agree with Beer_Slayer: scrub it with bore paste – this should smooth things out a bit and keep it from fouling quite so quickly.
Keep the barrel clean and you probably won’t have any problems at all (it’s not like a M44 is a match rifle anyway!).
For the price, it still sounds like you got a pretty good gun.