Bhagavad Gita says one who worships someone other than Lord Krishna is actually indirectly worshipping Him because He resides as the Indweller (Antaryami).

In the Kaushitaki Upanishad also, there is a story called "Indra's instruction to Pratardana", where Indra tells Pratardana to meditate on Indra as the supreme Brahman. 

So if Pratardana can get moksha by meditating on Indra as the supreme Brahman, why can't others? 

What does Sri Vaishnavism have to say about meditating on Devatas (and not Vishnu) as the supreme Brahman to attain Moksha?