It is for absolute pressure.. If Pg=Pa+C where Pg - gauge, Pa - absolute and C just a constant and Bernoulli is true for Pa, you have Pg + Pg*gh + 1/2Pg*v^2 = Pa + C + Pa*gh + C*gh + 1/2Pav^2 + Cv^2 = K + C + C*gh + 1/2Pa*v^2 = K' + 1/2Pa*v^2
You end up with an extra term on the right side, proportional to Pa and v^2, which means that you cannot determine the whole relation solely based on Pg.