Pretty much, yes.
I think Turtledove got it right that an early CS victory gives Maxamillian's Mexico a better chance of survival, as well.
But even if Sonora and Chihuahua don't become part of the CSA they are going to be dependent on the CSA economically, just like how they are with the US IOTL.
That is true, albeit likely less so. I imagine Maximilian's Mexico would be more stable and thus more economically succesful than OTL's Mexico, so that dependence may be lessened.
Personally, I think that Pacific ports for the CSA via purchases/conquests ranges from unlikely to impossible.
If the CSA managed to survive, they would almost certainly try to help prop up Maximilian alongside the French, seeing as how the Republican faction in Mexico was pro-Union. And the USA would likely have less of a border with Mexico, so it would be much harder to "lose" large shipments of weapons for the Republicans. Maximilian would likely then triumph, and the SME would become closely aligned with
The alternative is a French withdrawal and Confederate apathy allow for a Republican victory. I would imagine in that case, the USA and Mexico would grow much closer, perhaps even to the point where any Confederate-Mexican war would bring the intervention of the US. Even without an alliance, the US would likely be against Confederate expansionism, so I would imagine that the CSA would avoid war with Mexico as best they could.
And in any case, I highly doubt Mexico would want to sell more land to a USA-like American state when the humiliation of the Mexican-American war still hung around in their minds.
So yeah, I think that the only way for an independent CSA to get to the Pacific would be by holding its Arizona (and possibly its New Mexico) territory(s) and inciting/supporting a rebellion/pro-CSA movement in Southern California.