Are we talking about "In Heavens Graphic Overhaul" or about "In Heavens Cartographic Map"? Because those two are completely different mods. I mean they do the same thing, graphic overhaul of the map, but look quite different...
Using Cartographic and HIP together is possible and it works without any errors, that I know of, only it looks ugly. Like two different maps interposed one on another, because that is what it really is, texture from one map put over the other map... however, if you delete the mentioned files, then you get the map that doesn't look exactly like the original Cartographic mode map, but something like that... however, with some basic skills and knowledge you can make it look (almost) exactly like how Cartographic was intended to look.
In Heaven's Graphic Overhauld I haven't really tried, but from what I have seen it adds or changes quite more things so I guess it is either completely incompatible or requires some extensive modding to make it work with HIP.
I guess you could install HIP without LTM module (that is another map retexture) which would leave you with vanilla looking map,and then put IH's Graphic Overhaul on top of it. Not sure how and if it would work with SWMH map, but I assume it should not work flawlessly because SWMH not only adds provinces, but changes the map (no India) so dimensions are different, and you would probably end up with the same problem as with Cartographic + HIP textures for two different maps being put on top one another. However, I never tried and tested it, so you should really try it and see what happens.