Notice that this new forum section was just created yesterday and the subjects were migrated from the normal course of dialog where the Carbide guys are gonna focus attention and/or reply. I'm unclear if they consider touch plate or conductive probe operations as supported operations, however due to the current location of this discussion I'm leaning to "unsupported" nature of an operation like this.
I just measured my PROBE inputs, and sure enough, 3.3V. Your low level input reading smacks of something wrong or misconfigured. Unsure how the UNO ports are protected (if it all), but I'd guess they're pretty standard when it comes to low-level mCU. I've done a lot of embedded PIC and MSP430 development and both of these platforms provide TRIS/Port setup for ins/outs/pullups/pulldowns/etc... certainly Arduino family mCU provide similar operations.
I've run the Triquetra G-Codes via UGS with my v2.3 CC controller and had success that way... someday once I'm ready to dive in I'll roll up sleeves and get familiar w/G-code...