I've seen two green dots that should fit the Hellcat Pro without an adapter plate:
1. Swampfox Sentinel Micro Green Dot (available in both manual and auto brightness models)
Amazon Swampfox Sentinel Micro
2. Crimson Trace RAD Micro Green Dot (auto brightness only)
Amazon CT RAD Micro Green
Of the two I'd personally go with the Swampfox manual since I don't really trust auto brightness sensors
That being said, I have an S&W Shield Plus with a Holosun 507K mounted with a C&H Precision adapter plate which as you said cannot co-witness because of the plate height (I'm considering getting suppressor height sights haven't decided yet), works great but the plate cost me an extra $50 or so.
In a pinch you can always use the "top of the viewing window at the neck line" trick, place the top of the viewing window at the neck line of the target and you're going to hit center mass at 3-7 yards (results may vary beyond that distance).
Also have you checked for 3rd party suppressor height sights for your Hellcat? Looks like Night Fision might work:
Night Fision Optics Ready Stealth Series for Springfield