Hello,
FMOD is in fact free.
While the software is free to download, it is definitely not free to use in your game - whether or not you actually sell your game or make it a free download. Check the licensing options on
FMOD's website. Have you checked the new FMOD Studio, by the way?
Audio middleware like FMOD and WWise definitely make sense for bigger-scale projects, but for most purposes like small-scale indie and/or mobile games a conventional approach (linear audio) will suffice, especially in 2D games.
I've worked on a few Unity3D games that use Unity's own trimmed FMOD engine - pretty cool what you can do with that alone. (reverberation, filtering, 3D panning...)
More often than not I've noticed programmers telling me "do whatever you want" without direction or feeling.
I've made quite the different experience: my clients usually knew pretty well what kind of mood and instrumentation their game needs, even though they may not be able to put it in "technical" terms - but here's where exchanging references and providing layouts can help a lot. The conceptual phase is probably the most crucial one!
Of course, I always welcome if devs show an interest in adding small sonic details that improve overall fun and immersion.
But I consider
spotting (like it's called in the film industry) part of my job as a composer as well as a sound designer. Get an audio guy who shows an interest in more than just throwing assets over the fence, and be open for ideas!
I have no idea how sound designers work.
If you want a good overview of a game audio person's work and thought process, I recommend giving Aaron Marks'
Complete Guide to Game Audio a read.
Cheers,
Moritz