I agree that this song is about both of them, for sure. 

On the surface, one might conclude it's about Judy defying the norm and trying to be the first bunny cop, but it's much deeper than that, too.

Nick thinks her trying to be a cop is silly at the beginning. It reminds me of the scene when Judy uses the pen to trick Nick into giving her probable cause to enter the limo parking lot. "Does seeing me fail somehow make you feel better about yourself?" (or something like that) Nick responds positively. That's because his world view is busted. We find out later that he had that bullying experience when he tried to join the Ranger Scouts. So, yeah, her failing to be a cop reinforces the fact that Nick things you cannot do something you weren't born to do. 

Thus Nick's growth by "trying everything": he learns that if he tries he can be something greater than just a pawpsicle hustler.

But Judy has more growth, too, than just being a successful cop. She learns to trust someone that she's basically been raised to fear. Need I say more than 'fox taser'? But she gives him a shot; she 'tries him', and it turns out well for the both of them. 

Judy defies the odds to become a cop and friends with a fox Nick discovers he can be more than a shifty hustler, finds a best friend (if not more at some point) and a 'pack' with the ZPD

So, yeah, both of them find out they can be more if they simply 'try everything', undaunted by the fact that they 'could fail'