I was reading through the forums and it seems like a popular option is it buy a low end thermal monocular and an entry night vision scope for about $3k total.

After further reading it seems like hogs can see the light from an IR Illuminator. There us some debate whether hogs can see the 850 spectrum ones though.

Any insight to this?

Also, if I were to buy just a thermal scope, would it maintain zero while taking it on and off to scan or just spend extra on a clip on?

If you are using an IR illuminator, the glow from the illuminator can be see by hogs unless you have one of the 'black' illuminators that I believe is up around 950 nm and then the hogs don't see anything. It may have to do with the make and manufacture as well to be "black" but I have yet to see anything 900 or below that doesn't have a slight glow that can be seen. At 850, they can definitely see a glowing cherry.

Note that the higher up you go in NM, the more power you need to get comparable distance of shine (which is not see by hogs anywhere in the IR spectrum). So an 800nm will outshine an 850 will outshine a 900, all other variables being equal.

The ability to take a scope on and off in order to scan has to do with the mounting system more than anything else. You can do that readily with some scopes like the IR Defense IR Hunter MKII and some of the clips. Supposedly, it should work for the mounts used by Armasight, but I have not found that to be consistent and consistency is the key. Pulsars are bolt-ons and so won't work for your cause. Not sure about the FLIR RS series or ATN scopes.

You can see all the LED illuminators 940 and down ...or at least every one I have seen you can. The 940 is dimmer than an 850, but you can see it....and yes, the 940 has less range. Hogs will bust on these from time to time, but it isn't a deal breaker to keep someone from getting in the game.

A digital scope with low end thermal monoc is a fairly popular setup. Just expect that ID at any sort of range is more difficult with the lower end, low mag, lower res. monoc. Depth perception with thermal takes some getting used to.

I would personally stay way from clip-ons. Just my preference.

UltimateNightVision.com offers what is advertised as the only true return to zero mount for ATN scopes. http://www.ultimatenightvision.com/ATN-ThOR-QD-Mount-p/dloc-thor.htm

I have never trusted any scope to remain zeroed after removal and re-installation, but I just want to err on the side of caution.