Will you still be admitted without any hassle? Yes, you will! But, of course, you will have to settle with the hospital for the difference at the time of discharge.
Both Bumrungrad Hospital and Bangkok General Hospital (BGH) verified this process for us.
This is one of the advantages of purchasing medical insurance through a locally based insurance company that has a large selection of participating hospitals. You just show the hospital your card and you get admitted without any delay.