Any hosting company that lets you install your own software can host an OpenACS site. However, you are then responsible for pretty much everything - upgrades, making sure your data gets backed up properly, etc. They usually won't help you if you're having problems; it's caveat nerdor, as Philip used to say.
Also sometimes these small companies are many levels of reseller away from the network providers, and their uptime and network speed are not always very good.
If you're up for being your own sys admin, and don't need commercial quality uptime, these places will work fine.
