Fella is on target as always.

I just wanted to add that if you do use the non diversity antenna you will want to makes sure it is attached to the primary bulk head of the access point. It is labeled...

The AP is to used for outdoor deployment, I would reckon diversity shouldn't be much of an issue in this case.

Would putting a diversity patch antenna with a non-diversity patch antenna on the same AP have any complication to the RF signals? Any degradation?

No, but you be wasting money. And, you'd have three "tails" and only two places to connect them.

Diversity has a place for outdoor use too; for example, in a dynamic environment (like where people or other bags of water are walking through your RF field), diversity gives the AP a "second point of view" and an opportunity to resolve a clear path sooner (i.e., less likely to miss or drop a transmission).

We'll leave birds out of the discussion for now, I think you get the idea.

If you choose to implement diversity (IMO, you should use it, because you are more likely to need it than not need it), the antennas should be of the same type & gain, and they should cover approximately the same area.

If you mix antenna types or gains (gain is a function of the radiation pattern, so it should match as closely as possible), you will degrade the performance to some degree.

Good Luck

Scott