Since the question is "can I" I would say yes you can do what ever you want they're your fish. If you asked "should I" or "would you" you would get a completly different answer.
Exactly my thoughts.
With regards to water parameters .......... the water in the crater lakes of Central America (where A. labiatus originate) are for the most part the same as Lake Malawi. This is a non issue.
Diet is another non issue if you choose your main staple of food wisely. I feed the exact same food to mbuna (even those classified as strict herbivores, such as Tropheops macrophthalmus ) as I do Amphilophus species such as A. labiatus, and have never lost a mbuna to bloat. The biggest problem would be ensuring that the mbuna don't over eat while attempting to get enough food to the much larger RD. Pellet size that would work for both species isn't going to be easy once the RD matures. You can mix pellet sizes but the mbuna will constantly over eat, which makes for fat unhealthy mbuna.
The reason that I personally wouldn't mix the two would be due to aggression/size/behavioural issues, which in many cases will lead to excessive stress in one or the other, or both. IMO it's just not a good mix of fish.