Are enable rules supported for OOB CRM ribbon buttons

I have an entity A which has a 1-N relationship to an entity B.
When I click on the relational nav. link in the form for entity A it renders a subgrid containing instances
of entity B and the Ribbon switches to render the "SubGrid" specific buttons.

Is there a way to set up an Enable rule on the SubGrid for entity B so that the "Add New B" ribbon
button can be enabled via a custom JS rule?

I've created a command, set up an enable rule to execute a custom JS function and associated the command
to the "Add new" button in the subgrid form using the Ribbon Workbench but the JS function does not execute.

Are enable rules supported for OOB CRM ribbon buttons?

-Abhijeet