You can use graphics edited with PicMonkey for commercial use so long as it is a derivative work. A derivative work adapts and modifies pre-existing work in such a way as to create a new work. For example, you can use one of our graphics or stock photos as part of your design, but you can't sell just the graphic or stock photo as if it were something you created.
More info can be found here: https://www.picmonkey.com/legal#tos.
If you'd like a little more clarification on your particular project, please feel free to send along an example to the support team.