Not hypoallergenic, but they sure don't shed like my mom's Mainecoon.
As someone who has/had Ragdolls (very, VERY similar to Maine Coon, and also "rumored" to have been bred to be hypoallergenic--with people even posting "proof" about diminished enzymes or proteins or something like that, but then from what I understand the original breeder was somewhat of a madwoman)...
One of my ragdolls shed very little. His hair rarely attached itself to clothing. Most* visitors did not report any trouble with allergies. I think his shedding was less than Duma's, but then he rarely needed grooming and Duma needs a good brushing now and again even though he hates it.
The other ragdoll sheds like hell's bells. There are floating tumbleweeds everywhere, and his fur sticks to everything, even leather. It is more likely allergic people will say something about allergens although I don't know for certain whether this is due to the hair they see floating about (yeah, it's icky) or what they physically feel.
Same type of cat. Different fur. YMMV.
Most* does not mean all.