They can become very accustomed to being handled and my thoughts are that if they walk into your hands and your percipient at ensuring there is no chance of chemical residue on your hands then its fine to do.

Ensuring hands are washed and rinsed so things like hand sanitizers are removed completely is a must.
Also, having to catch a frog to handle is a stressful thing for the frog, so if the frog is reluctant to be handled then it shouldn't be handled.

Although my WTFs would come right to me at feeding time, I didn't handle them except to check them out occasionally.
Just my thoughts on the subject.