No, totally not worth it in terms of potency. IV dilaudid really doesn't last long for pain relief either, in my experience. I don't IV at home but in the hospital I was initially put on an every-2.5-hour schedule with the IV dilaudid and it would wear off in two at best. There's some cross tolerance that needs to be taken into account, but all other things being the same 10mg of IV oxymorphone is worth about 14-15mg of IV hydromorphone. You don't say if you're IVing 10mg (or more) at a time, but either way it's not a very fruitful conversion in the direction you're going from. I don't have to tell you this, but IV oxymorphone is really effin strong.
So I'm sure you're not in the mood for a lecture and I swear that's not what this is, but have you considered plugging those instead? I hear you that the medication is necessary for pain relief, but it also seems like you're in that nebulous place that a lot of pain patients end up in where you're abusing the meds and possibly addicted while still legitimately needing them. I've made myself pretty cozy in that place, too. Yeah IVing is about the least safe way you can be consuming those drugs but it's also the least efficient for long-term pain relief. I don't have any first-hand experience with IV oxymorphone (frankly I'm glad of that fact) but I doubt it lasts a whole lot longer than IV hydromorphone. Plugging should, and honestly can be almost as good as an IM shot with certain drugs. I think it's worth trying at least once to see whether or not it's still a possibility. Maybe it's not; maybe now that you've been IVing it will be hard to get much relief doing anything less. That's a pretty common issue, of course. I don't know... maybe I'm not telling you anything new, and I know some people simply won't do it. But this is a harm reduction forum, IVing is definitely not great, plugging should last longer if not as strong, and all around it's a step down in risk specifically from what you're doing now. If you won't do it, you won't do it, but at least it's not going to be because I didn't say something. Any time you can avoid the needle when dosing is a good thing, but that's the last I'm going to say of it. I'm a pain patient and an addict so I do know where you're coming from as much as I can because of that relatively broad commonality.
TL;DR: 10mg of oxymorphone is indeed way stronger than even the equivalent milligram amount of IV hydromorphone, so if that's how you're going to continue using your medication then it's not worth a switch. Plugging should be considered for longer pain relief if it's as necessary as it sounds, even if it's only sometimes and not your primary method of consumption.
Just out of curiosity, are you also on ER meds, or just these?