I don't know if flamethrowers were used that much in the battle of stalingrad, but I'm quite sure that Molotov Coctails were NOT used en masse by the germans or the soviets. I think only the finns mass-produced those molotovs (maybe brits too, I'm not sure), but you wouldn't be able to imagine my face when I played Call of Duty 5: World at War, and saw that all the soviet troops carried like 3 molotov coctails with them and used them as anti-infantry grenades.
Also, molotov coctails were more effective against early war tanks, such as T-26, because their exhaust pipes (or whatever they were) weren't as protected as later era tanks.
And again about the flamethrowers, I'm not sure if they would be useful at all in the game, also, they'd be very hard to model. You have the PPSH-41, so you have the weapon for those close quarters building raids, grenades to empty bunkers. If you had flamethrowers, you'd have to think about how it first of all would ignite stuff (after all, they used fuel, so it's not like using a lighter which doesn't leave any inflammable stuff after it, it just uses butane or another sort of gas. So getting actually hit by the fuel would sort of be certain death, but also, since the flamethrower isn't like a machine gun, it doesn't have bullets that hit and kill, it has also what you'd call an area of effect. Also, the flamethrowers of that era wouldn't really be very good, since you could do continuous firing for just a couple of seconds, also, if I'm not completely wrong, they had 2 man teams for a flamethrower, since it's a very heavy weapon.
In my opinion, flamethrower isn't worth the work for the game, also, it'd be a huge question about realism and balance, and another opinion: Molotov Coctails have no place in the world of Red Orchestra, at least not the stalingrad-sequel.
Please correct me if I'm wrong, I'm not a huge history buff after all.