There is signage, usually, at the resorts, stating that parking is not provided for park access. This basically means that no, you can't park at BC and then head to Epcot (or any other park) for the day.
Will they 'catch' you? Maybe, maybe not. But, that isn't the issue. The rules have been stated, one should follow them.
A quick story. While at BLT last month, I sat on my balcony, overlooking MK, the monorail, and the parking lot. I watched, every day, as security drove around that lot, very slowly. Evidently they do it several times a day. When the driver would get to a particular car, he would pull over, check it out. Then, he would either get back in his car and continue on, or he would pull out a pad of paper and start writing. I assumed that he was looking for parking permits for BLT/CR.
I watched, one night, as several groups walked over from the MK, after the fireworks, and got into cars, in the lot below me, and drove away. On one occasion, when a group got to their car, one person stopped, walked to the front of the car, and took something off the windshield. I have no idea what it was, but I know that car had been there all day. It was pretty unique (due to it's color), so I had noticed it before.