Is there a way to write an mdx query that could list the members on a
single dimension where a non-missing, non-zero datapoint is
populated.

I have six dimensions time, scenario, currency, year, entity,
accounts.

I know the scenario value is = ECO

I want to produce the unique list of accounts used across all
permutations of time, currency, year, entity, and ECO.

new to mdx so excuse me if this is obvious.