I’m also including a dll and other resources in the plugins folder to make the library work.
Can I include Math.NET Numerics in some code of my asset that I'm going to sell in the assets store?
Yes, of course you can. Didn’t you read the licence information when you downloaded the Math.NET library? It clearly states:
Math.NET […] available for free
under the MIT/X11 License.
The so the license in an MIT compatible license and doesn’t have any restrictions besides that the license have to be shipped with the library. Besides that you can include it in any work and sell it as you like.