Are most Salvias (S. luecantha for ex.) self fertile?
Except for the possibility of Salvia oxyphora, any sage growing in the wild will set seed under the native conditions. Some do so much more easily than others.
In North Carolina, S. leucantha does not set seed, but the presence of hybrids like Waverly, Phyllis' Fancy, and Anthony Parker (found as a volunteer in Beaufort, SC) indicate that there are conditions when it is possible.
The wrong pollinator, a too-short bloom season, or sudden changes in weather can cause pollination and seed development to abort. Carpenter bees (bumblebees with shiny black bums) are responsible for defeating pollination and seed set by their habit of puncturing flowers at their base to get a short cut to the nectar. Such flowers thereafter will not set seed under any conditions.
Self-incompatibility is possible, but probably rare. I have multiple forms of both S. puberula and S. involucrata that bloom at the same time, but none of these set seed for me here. In California, the Mediterranean, and Argentina, they might set much more seed.
Interesting! I know about the many hybrids. I have had an S. leucantha for yrs in Northern CA that has never produced any seeds. I am now assuming it must be because of the carpenter bees since they are everywhere. I have noticed their habit of cheating the system to get the nectar but I did not know that this negates seed production even if the flower does get pollinated. I now have the plant growing in Southern CA and it has produced seeds in the presence of a few different Salvia neighbors. There are no carpenter bees here at this time of yr go figure. I'm gonna plant the seeds and see what comes up. If it comes out an S. leucantha I can assume it is self fertile. If I get a hybrid, well hopefully it will be something nice.