It does. You're right that a refundable tax credit provides an amount equal to the value of the credit, which is independent of the individual's tax burden.
The medical expense tax credit is a credit that actually can be shared among family members. With regard to an individual who pays for the medical expenses of their spouse or minor children or another dependant relative, those amounts can be shared between spouses, for example. There's a certain amount of sharing that's done under the medical expense tax credit that's not available for other credits.