"Could" is a hypothetical question.
Of course EMS Madara "could" beat SM Hashirama. He might take him by surprise or score a lucky hit, Hashirama might make a mistake, get a heart attack or whatever.
But excluding these possibilities, then I have to answer : yes, he could. I'm gonna explain, but let's start with Kurama + EMS Madara.
Of course, Madara was destined to lose that battle - because Hashirama was the first hokage, and the battle in the valley of end was supposed to be "a fight for the hokage title" (even though it later turned out that it wasn't for the hokage title). Back then, during the Konoha invasion, powerscaling was much different than later in the story. Hashirama and Tobirama were supposed to be at "full strength", with Minato being the strongest hokage of all times (hence why Sarutobi desperately tried to stop the third edo tensei, even though, no matter what, 3 vs 1 is still better than 4 vs 1 (counting Orochimaru)).
When Madara started to become "antagonist", he had to be very, very strong....But someone weak shouldn't have beaten him so easily, right? Anyway...Madara's worst mistake was going "head to head" with Kurama and Susanoo armor against that huge arse Shinsusenju buddha statue. If he actually pulled back (even though it takes a lot of chakra to control Kurama + use Perfect susanoo at once..) and shot a huge bijudama with susanoo sword at that buddha, we would have had an insta kill (Hashirama hasn't really shown us any space time ninjutsu to teleport something that huge away...or to escape himself).
So let's get to EMS Madara without Kurama vs Hashirama without plot. IF Madara's susanoo can fly (like Sasuke's and Kakashi's), then he could just use intelligence and flight to fly and "throw" susanoo blades at shinsuusenju. Hashirama's only way, in this case, is to somehow bring down that susanoo (with a long range attack, like "shooting" those shinsuusenju hands at susanoo) or to let Madara use up all his chakra. Provided that those things don't happen before Madara smashes shinsuusenju to pieces (that would take some minutes), then Madara would most likely win.
So again..yes, he COULD beat him.