Splice 2 6x6 beams in Simpson CCQ
The Simpson bracket is not designed to transfer tension loads, that is absolutely correct. However, there are no tension loads on a beam over a post subject only to vertical loading (weight). So that is not a problem, except under very unusual loading conditions such as impact (the pergola gets hit by a car), or exceptional wind conditions (the pergola is struck by a tornado). Under those conditions, it is possible for the beam to go into tension, and the splice over the post could fail under those conditions, but if either of those events occurs, you have bigger problems than a failed joint.
If this were an inhabited structure, it might be a different story, but for your use as you described, the butt splice using the post cap is fine.