The anacharis is great to have in there with with him- it'll help suck up ammonia. AQ salt helps stimulate new growth of fins and tissue over wounds by acting as mild irritant. It is a good choice for minor wounds and minor fin rot, especially if one wants to avoid the use of meds. It can be used for a maximum of 10 days (because too long of salt exposure can damage the kidneys) at a dosage of 1 tsp per gallon, increasing to 3 tsp per gallons at the max dosage. The salt is pre-dissolved (very important- undissolved salt crystals can burn) in conditioned water and added slowly over a period of hour. Your cory cats are sensitive to salt, so I would never dose your 10 gallon with salt.
In your case, don't use the salt. He's already got meds and salt would be just another source of stress. At this point, it's the meds that are going to get him better- any advantages of using AQ salt would be weighed out by the stress they would cause him in addition to the stress that meds cause.
However, once his red spots go away and his fin rot is no longer spreading- e.g., once he's no longer on meds- you can go ahead and add salt to help speed his recovery. Give him a couple days in between meds and salt to regroup.
What you can do now to speed his healing: Get some rooibos tea bags at the grocery store. It must be 100% pure rooibos, no added flavors. Plop a teabag in his tank, leave it there until you can't stand how dark his water is getting. The tannins in the rooibos will help soothe him and promote healing. Indian almond leaves are even better than the rooibos, but they have to be purchased from Asia on ebay- IAL is great to have on hand, though, for the future. Here's a thread on rooibos
if you want to know more.
Make sure he's getting high quality food. Omega One betta pellets or New Life Spectrum betta pellets for his staple source of nutrition. Frozen bloodworms are a great source of protein (and protein is what he needs right now) and will make him very happy- good to use once or twice a week. (In fact, your corys will love you for it, too.)
How is he doing? Behavior still normal? How are those red spots on his body?