The Defender-ST would be a compatible option with your M18, as the slide is cut to otherwise accept the DeltaPoint Pro footprint, employed by the Defender!
Unfortunately no. The Hellcat would work with the Defender-CCW, however, and it would be a direct-to-slide fit, otherwise!
The Vortex Viper 1x24mm 6 MOA Red Dot Sight will include screws that will be compatible with most Docter adapter plates but may not be compatible with all. I would recommend using the included screws first to test fitment, if they work fine then you are good to go. If not, I would recommend the Swampfox Ultimate Red Dot Mounting Screw Pack, which can be found by using the link below:
https://www.opticsplanet.com/swampfox-ultimate-red-dot-mounting-screw-pack.html
The Vortex Viper 1x24mm 6 MOA Red Dot Sight uses the Docter/Noblex footprint. To mount it to a Taurus TH9 you will need a dovetail mounting plate that fits your rear sight dovetail. The Taurus TH9 uses a Novak rear sight cut. So the dovetail plate at the link below might work but I recommend contacting Evolutionary Gun Works to confirm compatibility.
https://www.opticsplanet.com/evolution-gun-works-vortex-viper-venom-fits-burris-fastfire-and-docter-1-811-in.html?_iv_optic-cut=novak
This optic is indeed compatible with the OSP system, however, a replacement set of screws specific to the OSP is required, which are available through Vortex Optics at no charge. Please contact Vortex at 1.800.4VORTEX, and we can get you taken care of!
You can absolutely mount the Viper on an AR-15 using the included Picatinny base, however it is best used with a Riser like the one linked below.
https://www.opticsplanet.com/vortex-razor-red-dot-ar15-riser-mount.html
Yes, the Vortex Viper 1x24mm 6 MOA Red Dot Sight will mount to a Canik METE SFX. The Vortex Viper 1x24mm 6 MOA Red Dot Sight uses the Docter/Noblex Footprint, so you will need to use the corresponding mounting plate from Canik.
The FDE is not currently available for order at the exact time of this response.
The Viper red dot will fit your R1 with the use of a rear sight replacement dovetail adapter such as the following:
https://www.opticsplanet.com/evolution-gun-works-vortex-viper-venom-fits-burris-fastfire-and-docter-1-811-in.html?_iv_gun-model=1911
Call EGW directly at 215-538-1012 to confirm the correct part number before ordering the mount from Opticsplanet.com
You will require an adapter that replaces the rear sight with a mounting plate that will accept the red dot. We do not currently carry any adapter plates that will work for that handgun.