The state program will have a list of approved lenders, and normally you'd have to select one of those approved lenders. The reason being is they are specifically trained on the down payment assistance program.
I work for a national home builder. When our preferred mortgage partner cannot help a buyer client with the application process for downpayment assistance programs, we allow the buyer prospects to use their own source and still collect the closing cost assistance that we offer. Occasionally, good assistance can be had from real estate agents who have closed transactions involving down payment assistance programs.