Have heard conflicting reports. When I went last Nov, it let me overlap my original 3 FP+ selections with ADRs with a warning, but when i tried to adjust and optimize the FP times it would no longer let us overlap, which was a big pain because we had a bunch of 11:30-12:00 lunch ADRs that blocked out 11am-1pm FP+ selections. Have heard others report successful overlaping with a warning. If it is a non-popular restaurant, you could always cancel the ADR and rebook after FP+ are made at the 60 day mark.
Be interested in others more recent experiences.