The freeze with the card uninstalled would seem to indicate against it, but on these G3 upgrades, if the machine freezes during extension loading, it is often a defective cache on the upgrade card.  The cache isn't active until the extension modifies the PPC750 register settings.   When the cache is activated and is also defective the machine freezes.

I had a NewerTech NuBus upgrade (goes in PDS slot of x100 series) with this symptom.   I pulled the heat sink off and the factory applied heat sink grease had a trailing line which crossed the pins of one of the cache chips.

The last time I checked, DigiKey still had compatible cache chips available, in the event that you want to risk some money trying to replace them.