It all depends...

YP often get over eaten when in ponds with LMB and can't maintain their numbers long term. You either have to restock advanced YP(8"+) every so often or they slowly dissapear. Rarely will YP overpopulate and stunt in ponds with LMB, I can think of only one pond like this. BG in northern ponds often overpopulate and stunt in ponds, even with LMB. That is why it's important to time your stocking of the different fish at the correct time and the correct sized fish.

Keep in mind koi are in fact common carp. They are just selectively bred for bright colors and in some fancy scale patterns or showy fins. Koi also seem to generally reach smaller sizes and grow slower than their wild genetic borthers. However, they are fertile and will reproduce in ponds. Often their bright colored young are controlled by LMB predation. However some of those yound may display more cryptic coloration than there parents. They are less susceptable to predation and may survive to spawn. A few generetions later, you have cryptic colored koi very similar to common carp making a muddy mess of your pond.

I enjoy koi. I have one as an entertainment fish. No other koi to breed with, he's bright yellow and has butterfly fins making him striking in the water. If I added others, I could risk them spawning and creating a mess. With plentiful bass and limited cover, they may never have YOY survive to adulthood. You just have to ask yourself if you're willing to take that risk to have more than 1 koi in your pond at a time...