Oscilloscope over-current protection
If I understand you right, you had 1.5A flowing into the chassis ground of your scope via a BNC connector?  If that's correct, it is unlikely to have damaged anything.

A scope chassis is a protective earth, and should be able to handle enough fault current to pop a breaker, so 1.5A shouldn't cause damage.

As for the 50 ohm input, yes, you can use a BNC tee with a 50 ohm termination on it.