Its worth using them together they dont counter each other, however when minoxidil is mixed with spironolactone it smells much worse so never mix them in the same bottle, just apply one, let it dry a bit, then apply the other.
You can definitly use minoxidil and spironolactone together - and they don't cancel each other out. I think (I don't know) your confusion might stem from reading about those who try to mix the 2 products together in the same bottle. That can cause several problems).
If you use the 2% spironolactone liquid, apply the spironolactone first, wait 10 minutes, then apply the minoxidil.
If you use the 5% spironolactone cream, apply the minoxidil first, wait a suitable length of time, and then apply the spironolactone 5%. (most use the 5% spironolactone as a before bed application).
You should check Dr. Lee's website. I'm pretty sure he has some background info on spironolactone and minoxidil use in one of his FAQs.
Some even use the 2% in the AM, and the 5% in the PM.