Penny stocks are those that trade at a very low price, have very low market capitalisation, are mostly illiquid, and are usually listed on a smaller exchange. Penny stocks in the Indian stock market can have prices below Rs 10. 

Yes, you will be able to invest/ trade in penny stocks (or rather Stock below price of Rs 10)  using Dhan, however this will not be available for all penny stocks. Only for those that are permitted as per the risk policy of Dhan.