I don't think it's at all unreasonable for Singapore to require that foreigners have some reasonable, minimum income (and/or wealth) appropriate to the financial realities of modern Singapore, in part to avoid substantial (not all!) risk of foreigners becoming state burdens. And I don't think governments should disfavor
or favor religious workers with such requirements.
The government already favors charities with
major tax preferences, but that's all the more reason why their foreign workers shouldn't be destitute or near destitute in Singapore.
As mentioned, I'm open to the idea of allowing appropriate, in-kind housing to count toward the minimum income requirement for S Passes. Housing is the major financial problem for foreigners in Singapore. If a religious organization provides appropriate housing, directly, that ought to count for something in my view. It doesn't under current rules.