Even though you're probably set in wanting to cover it up, I think you should let your marks show. The pictures are ABOUT your pregnancy. They're a part of it! You should show them off, in my opinion. :) but, otherwise, yes your photographer should be able to photoshop. If not, then I'd go concealer and powder just to be sure.
Also dermablend is awesome, can get it from ulta.
Its thick body make up
Your photographer can use photo shop if they are legit to cover them :)