Saruman and betrayal

[Kuruharan]

I think Sauron would love to see the good side fighting with someone who was supposed to be one of them. Now, if the battle looked like it would be one sided against Saruman, then I can imagine Sauron trying to help him even the odds in some way, but it wouldn't be to save his life. It would be to spill the blood of his enemies.
-the phantom

I think the question or not Sauron would go to the aid of Saruman could be answered by part if we can come to a consensus on the the characteristics of Sauron the entity.

Was he a primeval dark deity of chaotic evil in which blood and destruction was the ultimate appeal and desire? Or was he a quasi-ominipotent entity of conscious sentience and logical thought, in which he had a plan and was working to it?

-and-

He was as I would submit, a master strategist of the art of maneuver - the quintessential Machiavelli of the books.
Saurreg

I think you both summed up Sauron's character accurately.

A review of the Tale of Years reveals that prior to 2953 removing Saruman would have been easy because Isengard was evidently unfortified. (One has to ask why, because it was originally intended to be a fortress...maybe the fortifications were allowed to decay to the point of being militarily indefensible...or something.)

After 2953 Isengard was fortified and presumably garrisoned, requiring military intervention to deal with.

Unfortunately, by that time Sauron was back in Mordor as himself and had his lackeys in Dol Guldur. I think we can say that he would have been militarily capable of intervening to save Saruman if he felt so inclined.