Of middleware solutions I've only used Wwise so I don't know how tricky using fmod can be, but if I was hiring someone I wouldn't care if they know the tools or not, but if they understand how game audio works in general. Part of it you will learn by learning the tools, but most of it comes only thru experience in other words doing sound design for games.
Ability to make good quality sounds is important, but equally important is knowing how to use them and coming up with interactive sound design solutions. For example sword impact sound in film is just a designed sample on timeline, but if you are doing a sword fighting game the sword impact sound is more likely metal impact sound + metal ringing sound + metal scrape sound all mixed differently and with different kind of release times depending of material it hits, velocity, angle of sword and so on. Sometimes designing systems like this is job of a programmer, but imo that's just wrong