It depends on the hotel--we've had the Entertainment Card rate honored by some hotels and not by others for the "park & fly" options.
I'm not sure which airport or what hotel you are using. The last time we flew from Detroit Metro, the Ramada Inn honored the room discount and we had a park & fly package. I believe we had 7 or 8 days free parking and paid around $60 for our one night stay with the discount. We did this at Ramada twice and during a Mom & Dad trip away we were upgraded at Ramada to a suite for the night.
Now, we've stayed at Fairfield Inn (Detroit & Toledo, OH) and they wouldn't honor the Entertainment card discount BUT the higher end Marriott would honor it. Further, I got a much better rate on Expedia for the Toledo, OH Fairfield Inn last summer.
We've also received Entertainment Club discounts on hotels that aren't even listed as being participants. We usually just ask when we're doing our research on where we will be staying.
Happy hunting.