Yes, Rotom-Mow is a good Pokemon to use in PU
At the time of this post, Rotom-Mow is in Tier 2 on PU's Viability List, basically being one of the "High" rank or one of the A ranks on a Viability Rankings. Rotom-Mow's typing and access to utility moves such as Trick, Will-o-Wisp, and Pain Split make it versatile. Rotom-Mow is usually used as a pivot, being used with either a Choice Scarf or Choice Specs, most likely having Trick on that set. If you look at PU's Role Compedium, you can see what other sets Rotom-Mow can use. Other sets Rotom-Mow can use in PU are Offensive Nasty Plot, Defensive Nasty Plot with Pain Split, or a utility (or physically defensive?) set with Leaf Storm, Volt Switch, Will-o-Wisp, and Pain Split.
TL;DR Rotom-Mow is a good Pokemon in PU since its typing can allow it to serve as a pivot with Choice Scarf or Choice Specs, both Choiced sets most likely using Trick. You can also experiment with Rotom-Mow and use sets such as a Nasty Plot set or a utility set.