You can by no means place ANY fish in your tank while you are treating for ich. IMO
the ich "medication" does not work anyway. The only true way to treat for ich would be hyposalinity or cupramene. Any fish that you put in your tank before you let the parasite completely die off will in turn get ich and so the cycle will just start over again. You really should quarantine your fish. The hyposalinity will lessen the stress to your fish while helping them out with the ich at the same time. You have to let your tank set for at least 4-6 weeks so the parasites can go through their life cycle and completly die off. I suspect that you don't quarantine your fish before you put them in your main tank but thats just a guess on my part.