Can I use this plugin in a commercial plugin for WordPress?
The software is under an open source license, which per the open source definition guarantees you may use it for whatever purpose you want.
The license used is the GPLv3, which is a strong copyleft license. It requires that if you distribute your software that includes this plugin, or make a derivative work based on this plugin, the entire work must be distributed under the GPLv3.
If you are looking to write a plugin based on this one to sell over the shelf, this might be difficult, because people who bought a copy of the software from you have the right to redistribute it for a lower or no fee.
If you plan on making something bespoke, selling it once, to a single customer, the GPL doesn't pose any direct problems.
The readme file of the project declares the project under the GPLv3. Be wary, anything that uses it is forced to be under the GPLv3 as well. This is a strong copyleft license.
The project however, doesn't actually include a license file, thereby making the project improperly licensed, and the GPL then legally doesn't apply to the project (if I remember correctly - as there is no link or place where people can find the license).