The same vendor offers just the water resistant monitor, so it would be possible to use an alternative camera that, for example, simply requires a hole in the plastic so it can fit flush. Ideally, I would prefer a waterproof, multi-input display such as the Pyle, but in a smaller size that could be more easily installed w/o being as intrusive. There are lots of cameras out there that have brackets that should easily fit just about any installation situation.
Looking at the pictures that sloride posted of the Slingshot dash, it doesn't look like the opening will accommodate a 1DIN (approximately 2" x 7" plus a small clearance factor) w/o modification. Depending on how hard it is to modify the opening, there are several marine-grade 1DIN stereo radios w/3-3.5" displays, some w/ dual camera inputs.
While not camera-compatible, the Clarion CMS2, the Milennia PRV16 and the Jensen MS30 are all either water resistant or waterproof and appear to require just a single 3" or so hole for mounting, although specific models may also require a main unit to be hidden somewhere else.
This would all be so much easier if Polaris had designed the dash with a standard DIN opening!