Yes and no.
In my experience, tapping is mechanical. This means that if it is done right, it works. Much like you don’t have to believe an aspirin will work for it to help your headache, if tapping is done correctly it will be effective whether or not the subject believes it will work. But there are a few important things to keep in mind.
1) You must do it correctly. For tapping to work, the person who is doing the tapping has to be tuned into issue being addressed. Just because you are saying the words out loud doesn’t mean you are tuned in to the problem.
I can be saying “This pain in my foot. This pain in my foot. This pain in my foot…” but be thinking about what is on TV tonight. If this is the case I am not tuned into the problem or following the tapping protocol correctly so it will not work.
If a person is skeptical they are less likely to commit fully to the process and there is a higher probability that tapping won’t work because they are not doing it correctly.
2) Understand what you mean by success. We call an aspirin a success if it stops a headache for a few hours, but we don’t expect to never have a headache again. Hold tapping to the same standard. It is very easy for a skeptic to dismiss tapping because the change isn’t permanent.