As a trauma nurse, I can tell you that if you end up in the ED in a really bad state, most patients in the US, anyway, will be put through CT scans, head to toe.
Via that, they'll definitely see the changes in your abdomen.
There aren't a lot of things they'll do to you *before* they'd do that scan... in the ED, that is. There aren't a lot of procedures where they'd really go in there right away. They might do a rectal if they think you have a spinal injury, but overall, unless the injury or worrisome issue involves your backside, most likely your pouch will be safe.
Can't say that would be 100% of the time, so a medical alert bracelet is still a good thing to have just in case, but honestly, your butt is rarely the focus in a trauma bay, unless again your injury or bad issues are involving your backside. And again, at least in the US, you're going to get scanned head to toe, and they'll definitely see that you're "not normal" in there.
And hopefully, family or friends would be there soon thereafter to give them your history.