Well, I'm no professional yet but I'm finding it pretty good coding in C while using the proper lintian together with clang, I also use the package script, which allows me to run the code from within the editor. If you give enough tweak, I believe it can be a pretty usefull IDE. Didn't try any gdb integration yet.
The languages Atom supports have very little to do with the languages Atom is built with. Anyone can add first-class language support to Atom and many have.
I watch all the new Atom packages as they are released, which is taking more and more of my time, and I have been shocked at how many languages there are. There are many many weird languages I've never heard of.
Its fine. I'm using it for: Go, Perl, NodeJS, Scheme, Bash, C++, and Rust.
You might have to add some of the syntax highlighting etc, but there are packages for most languages available directly in the built in package manager.