So hard to say... Most Californians are libs, so when you realize Arnold was voted in on a recall of a Democrat governor who was so freakin awful that Arnold Schwarzenegger was chosen by the majority of Californians to replace him... he is not going to be a true conservative by any stretch.
So for REAL conservatives, Arnold supporting somebody isn't some great thing. Problem is, even the registered Republicans aren't real conservatives for the most part. Tom McClintock - a pretty legit conservative Republican - also ran in the recall election but Arnold stomped him, and Arnold's politics pretty much match McCains, so that gives you an idea of where most Republicans in CA are.
It will be more interesting to see how Republicans in the northern part of the state vote (CA awards delegates for each district, not winner take all). While the Bay Area / SoCal Republicans are for the most part a big-government pro-war variety (read John McCain), the Northern Cali ones are where there is the most hope. The question is, as it is across the nation, whether the "real" conservatives will see Romney or as their only alternative to McCain, or if they see Paul as one (Huckabee will be a pretty big non-factor in CA, minus some communities in the Orange County/Anaheim area which is fairly religious).