RCA plugs/jacks can be (and are) used in power circuits. I tend to think of them as audio connectors because that's what I'm used to....
Approaching it from a theoretical angle what you are doing is joining two circuits. You can do this with a single wire; two wires that have been soldered; two wires mechanically joined by crimping/twisting...held together with a wire nut, vinyl tape and or goop for extra protection...whatever.
A connector like an RCA is just an easy(ier) way to tie two circuits together...most often in a way that can be undone and repeated with ease and without loss of material and too much time.
To make an obvious statement; Any method will work if it does what it's suppose to do.
1) Is it 'easy'?
2) Cost effective in time and material?
3) Able to transfer the "stuff" ( current, voltage, data, frequency, etc.) without getting in the way?
4) Sufficiently secure from interruption from the environment...anything from intermittent shorts, corrosion, gravity, or unintentional 'mishaps'
5) Whatever design criteria someone needs/wants...
If an RCA plug is not sloppy; makes a solid connection; does not have significant internal resistance; and you're not bothered by the positive making contact before the negative...what's the issue other than "It's an audio connector"?
