I think so.
Mermaids are female Merrow. They are viewed as a type of Faery (Faerie) by many, and are thought of in different ways. Some think they're benevolent, others not. Some believe they are fair and beautiful, some believe they aren't. Personally, I think all Faeries are very beautiful and wise.
I don't know if Merrow are real, but I am almost certain that at least some types of Faeries are real. My friend and I summoned a Faery once (the Faery will not come unless s/he wants to, of course--at least that's what I think) and though we did not see the Faery, the candle flared up and a tickling sensation ran up and down our backs, both signs that a Faery was near. We also felt something watching us and heard rustling, and we believe s/he drank some of the milk that was on the counter, as it decreased by about three centimeters.
There are two reasons we do not see Faeries: 1. They don't actually live in our Realm. They live in a world known by many names: The Otherworld, the Twilight Realm, and Faerie, just to name a few. There are believed to be Seven Gateways to the Twilight Realm. 2. You can not see Faeries unless you utterly believe in them and the Faeries choose to let you see them. So, if you gain the favor of the Faeries, you may be allowed to see them!
If you would like more information, feel free to ask! I would love to help. :)