I was a co-CTO for a small technology company. Having separate distinct roles is what made it work for us. Downstream, the roles are treated with equal authority and responsibility. Upstream (to the CEO in our case, to the board in Netflix's case), the roles have distinct areas of accountability and weight.

And similar to Netflix, our company had co-CTOs because we were mixing two different technology strategies for our software portfolio. The only awkward part was when leadership lost any confidence in one of the pair.