just wondering, on my iPad Pro 9.7 running iPadOS 13.5, could I connect a usb wireless mouse using the lightning to USB adapter? And will the mouse provide the same functionality as a bluetooth mouse would?
Yes, it should definitely be possible - and it should work with the same functionality as a Bluetooth mouse.
The Logitech unifying receiver presents itself to the operating system essentially the same way a cabled mouse does. Therefore iOS works for that receiver without extra "drivers" or anything like that.
I have personally used a Logitech wireless mouse with an iPad before, but I can't say if it is the same exact model of mouse, you have. You might experience that extra buttons for example have no function or similar, but the basics of pointing and clicking should work.
According to Apple, if you're on iPadOS 13 or higher it could be possible but devices can differ so the manufacturer would know best.
With the appropriate cable or adapters, you can connect various third-party mouse devices with iPad using USB and USB-based receivers. Refer to the device manufacturer’s instructions.
I recommend you contact the device manufacturer and ask them.