Is this really true? I have never heard this before. Could someone else confirm if this is regular procedure?
Yes, we experienced this in November. When we arrived at the TTC, they asked to see our resort ID before allowing us to pass on to the Monorail or Ferry. Since we didn't have a resort ID, we were told we couldn't board the Monorail or Ferry and we were held at the gates just behind the ticket booths!
A different day later, we had planned to have breakfast at the Polynesian an hour before EMH hours began. We walked to the Poly, had a quick breakfast, and were able to board the Monorail along with other resort guests. No request to see a resort ID from that point on, and we went through the turnstiles for EMH. That wasn't our intention, as we figured we'd be held at the turnstiles or on Main Street rope drop.
They check the resort IDs at the TTC as that weeds out all of the off-park guests when the MK opens for Extra Magic Hours. This way, they don't have to check the resort IDs at the turnstiles as only guests arriving from resorts are allowed to get to the turnstiles. It speeds up the turnstiles, while all off-park guests are fuming back at the TTC!
As far as avoiding the EMH park, as long as you have park-hopper option, you can enjoy the park early, and hop to another park when the MK gets packed! If you don't have park-hopper, I would avoid the EMH park.