Hey there.
The block plugin does not require YEP_BattleCore to work, but it does require YEP_BuffsStatesCore. It uses a function target.result().isBlocked() with BuffsStatesCore to activate the block effect from a react effect tag on the block state, meaning if you don't have BuffsStatesCore, while the actors' block rates and values can be seen and update, they won't do anything at all.
The plugin includes a sample txt file for a react effect note tag to get the desired block effect to happen. You can edit the react effect tag to add in other effects to a successful block as well. I had one in my old project where a successful block created a yanfly hp barrier equal to the damage that was mitigated, for example.