The hydrodynamics of the hull shape will be compromised with the indentation and will be a source of turbulence from that point rearwards. All things being equal it could mean the difference between winning and losing a race.
That dent looks like REALLY small to me in the picture. I wouldn't worry about any negative effects in the hydrodynamics department. Especially not when it is way back on the hull where there is alot of turbulance already anyway. The laminate doesn't look compromised either I would just sail the boat for the first period and then a few seasons from now fair it when you also are doing the other spots and boards.
I sail of the beach and can't baby tender my boat so I got bigger roughness then that on my keel line. Doesn't feel significantly slower.
Wouter
