Actually, judging by the shape of their masks, they probably can without too much issue. May have to crane their necks a bit.
My own gas mask is unwieldy when trying to see out of it and I did some shooting with it. But then again I have no training.
What type of mask do you have?
GP-5 gas mask and mirasafety gas mask
GP-5s can be tricky. The Hose really helps though. It all comes down to how high your sights are and how you angle your head.