Currently, I have string lights, on a screened-in porch, plugged into a zigbee outlet which is operated by an Osram battery-powered switch. Would like the ability to control the brightness of the lights.
Any other recommendations for less expensive, battery-powered dimmer switches that would control a dimmer outlet?
You can--once you get a device into Hubitat, you can make it do pretty much anything you want with any device by responding to events from one device (the Lutron Aurora, in this case) and sending commands to another (your smart plug, in this case). However, the Lutron Aurora is a bit odd; either the device itself or at least Hubitat's built-in driver stores/tracks an internal level, like a dimmer, so most people would "mirror" that out to a dimmer or bulb. I'm not sure what an intuitive thing to do with an outlet would be, but maybe turn it on if the level increases or off if it decreases, or just ignore those and use the button push to toggle the outlet instead.
If these were just button events (for the center button and maybe a start and release of turning in each direction), then this might be a bit easier to set up. But it's probably not impossible as-is, and I know there is at least one custom/community driver that may work if you don't like the built-in one for these reasons.
In terms of possible other devices, I'm not aware of many that sit on top of a switch without needing to change the switch itself in some way. The Osram/Sylvania/Lightify 2-button dimmer (model 73743) is one, but it doesn't appear to be available anymore. I've seen custom "mounts" for the Hue Dimmer that let it magnetically sit on top of a switch, but I have one and I'm not impressed with it--the magnet isn't strong enough, so the Dimmer flies off if you don't touch it softly enough (might be easily fix-able yourself, but I haven't tried). There are some that are meant to actually move the switch for you, like the ThirdReality Smart Switch (again, not really a switch itself--it mechanically moves the switch underneath). Then there are others like a Lutron Pico (Lutron Smart Bridge Pro or Main Repeater required) or Zooz ZEN34 remote that can fit in a standard rocker plate but would require hard-writing the switch underneath--probably not what you want.
Yeah! The Osram can work for that too; it doesn't have dimming per se, but you can set up an automation to respond to the button events and dim the dimmer as you want (a logical choice would be button 1 pushed = on, button 1 held = start level change up, button 1 released = stop level change, and similar for button 2). That's how I prefer to do it and is what would make the Aurora odd for some cases, though since you're using it with a dimmer anyway (I didn't read closely enough and just assumed it was a smart plug), that shouldn't be a problem, either--the built-in Mirror app makes that easy, or you could create your own Rule/automation.