First post here on this forum.
No. Every engine and generator exhaust should have its' own dedicated discharge port. Potential problems: when runnning both engines you might be causing too much backpressure on the exhausts; when running just the engine or generator, you could potentially be forcing water up the one that isn't running and get water into the cylinders. Plus if you have a survey done for insurance purposes or when selling, the surveyor will call it out and it will have to be fixed. Best to do it right the first time.