Do you mean young/immature coconut or mature coconut?
The macronutrient composition of the two differs quite a bit.
Young coconuts are low in fat (see: http://www.livestrong.com/article/277669-young-coconut-nutrition-in...) whereas mature ones are high in fat (see: http://www.livestrong.com/article/390337-nutrition-information-of-a...).
Yes, I think immature coconuts, which are mostly water anyways, should be okay with fruit, but I wouldn't mix mature ones with fruit due to their high fat content. However, I'm just basing my reasoning on common sense here, I'm certainly no expert on food combining ;-)