depends,
a recent board I layedout I did not put dedicated OPAMP decoupling caps on the supply pins, because the board only had two OPAMPS and the DC
C converters (+ their decoupling) were very close
Yes decoupling is used to minise the effect of of fast-edges and as you say you dont have any, but they are really needed for analogue IF the supply rails to the chip are noisy, if the rails are noisy then the output signal is going to be more noisy then you would otherwise expect.
for the hassle of two 100nF, I would put them down