I don't know how well skill against AI translates to MP. The few times I've played long enough to fight AI's I've been beaten somewhat consistently. Tactics used against AI v tactics used in PVP tend to differ some. Not that I'm excellent at MP either.
It depends on how hard your AI is. If you're facing overwhelming AI, you're forced to be creative. It won't teach you involved things like adaptive scripting, but it can be helpful for teaching you economy and squeezing every last drop out of your resources.
It also can be useful for making you much better at expansion, which really makes a difference in MP. It additionally can help give you a better idea of all the tricks in your toolkit, though it's easy to miss this by just figuring out what works and doing it over and over again.
The bottom line is that beating the AI mostly just requires you to be able to analyze how the combat AI works so you can exploit it. MP is more about being flexible, and working the human side of things, both in terms of diplomacy and subterfuge. Although the skills that help against the AI will still help here.
As long as you're adaptable, don't let it go to your head, and don't calcify the bad tactical habits that the AI will let you get away with, I'd say it's better to be good against (non-pushover) AI than to be a total neophyte going into MP games.