First of all, let me comment on the "gravity + QFT" statement. For sufficiently small curvatures, where we can neglect the effects of quantum gravity, we can treat excitations of gravitational field as normal spin-2 particles.
Exactly in this spirit the field of QFT in curved space was created. This theory describes well the interactions of ordinary particles with gravitons. It is an effective field theory that breaks down at some very high energy, when higher order terms come into play and cannot be neglected. The problem only occurs when we try to interpret the theory as a fundamental and take this cut-off energy to infinity, as this results in divergences at high energies.
Returning to your question, in the approximation of small curvatures i.e. in QFT in curved background, the interactions of gravitons are just like interactions of any other gauge field e.g. gluon, except that if couples to everything that has mass.