No, the CTS-1550 isn't waterproof.
The CTS-1500 is no longer available.
Yes, this will fit the Hellcat. This model will remain on unless the cover is on.
If you have an optic ready SCCY DVG-1, this Crimson Trace CTS-1550 3.5 MOA Red Dot Sight would be able to mount directly to the optic cut slide without the need for an adapter plate. If you do not have an optic ready DVG-1, you cannot fit this optic.
If the adapter plate you speak of is a Jpoint or JP Enterprises footprint, then yes, the sight will fit.
The Crimson Trace CTS-1550 3.5 MOA Red Dot Sight uses the Shield RMSc footprint and will not fit the optics cut on the Sig M17. The Sig M17 has an optics ready slide to fit the Sig Romeo1Pro and Leupold Delta Point Pro.
No, The Crimson Trace CTS-1550 3.5 MOA Red Dot Sight uses the Shield RMSc footprint and the Crimson Trace RAD Micro Pro Red Dot Sight uses the Shield RMS footprint.
You would need this adapter plate: KK-RMT-TYHJ-49402
Yes, the CTS-1550 will mount directly to the S&W Shield Plus without an adapter plate.
If your slide or mount is a shield footprint mount it will fit.