Yes, all three are metabolized by CYP2D6
From what I've read people who can't metabolize codeine into morphine still get some effects, maybe due to other metabolites (iirc only around 10% of codeine is metabolized into morphine). Oxycodone is active on its own and only around 5% gets metabolized into oxymorphone, so while oxymorphone is stronger it shouldn't make much of a difference. Tramadol is metabolized into O-Desmethyltramadol, a more potent opioid receptor agonist with NRI effects, while tramadol itself is a weak opioid receptor agonist with SRI effects, so if you're a poor metabolizer effects will be reduced