can metamers contain N as differing functional group?
This term is so old, I'd never even heard of it, had to look it up. Hooray for wikipedia 

https://en.wikipedia.org/wiki/Metamerism

. As i understand it, this applies to the two compounds you give.

The proper modern term is "isomer", a substance having the same molecular formula as a second one, but in different structural arrangement. (And yes, the two are isomers, although you would only rarely come in a situation where you want to discuss them as such, because they are chemically very different.)