So long as the rest of the piano is consistent, and the action, pedals, etc. aren't horrifically warped, you'll be fine, albeit anyone (pianist) who listens to him play will probably be annoyed. Recordings would be interesting to hear.
Many period instruments of Bach-Chopin, right up until about 1900, were at varying pitches and for that reason, give varying tone qualities. I actually just recently performed the first movement of the Beethoven Tempest sonata on a fortepiano of my teacher's; quite a difference, but not at all due to the tuning (~428 hz).
I'd be interested to hear some of his playing on this piano.
Cheers!