.45 Cal suppressors work fine on 9mm hosts, they're just typically a little larger than a dedicated 9mm can. Our all titanium and stainless steel Phoenix series, for example; the 9mm model is 1.25" diameter while the .45 version is 1.375" diameter.
https://www.eccomachine.net/product/phoenix-ix/
https://www.eccomachine.net/product/phoenix-xlv/
It's not a huge difference, but it can matter with some hosts, especially if you're not using an optical sight and there are no suppressor height sights available for your host pistol. Smaller cans may still occlude your iron sights, but the further above your sight picture the can body sits, the more difficult it is to superimpose with accuracy, and 1/16" of radius does make a noticeable difference.
As for using pistol cans on rimfires, if they're serviceable, it's not a problem, and they'll suppress OK, it's just more size and weight than most want to tolerate on .22 hosts. Most rimfire cans are around 1" diameter and 5-6" long, but they can be shorter, and we actually make one that's quite a bit slimmer:
https://www.thefirearmblog.com/blog/2022/10/22/ecco-machine-salamander-rimfire/
As a final thought, be prepared for the fact that a simple blowback .45 ACP carbine like the Hi Point is still gonna be pretty loud at your ear, even using ammo that stays subsonic out of the longer barrel and regardless of what can you use, regardless of how well it suppresses at the muzzle end. Semi autos that are actually cycling have ejection port noise, and simple blowback is almost universally louder than delayed blowback or locked breech critters. I don't have any personal experience with the Hi Point .45 carbine, but I do with our Marlin Camp 45 and others. It will probably be uncomfortable for naked ears.
