Substrate "tap" library elements, or a P+ contact nearby,
would be needed to pass DRC. But the substrate connection
happens all by itself in junction isolated P-handle CMOS, no
way around it. Everything that is not "something else", is
"substrate".
Now some PDKs do have neediness, like you have to put a
"bulk" polygon or some such thing before the extract rules
will work right. I haven't used this "ams35" kit, to say. But
a well done PDK should have such things documented,
either in the verification stuff, the layers descriptions, or
both. Again, though, I don't use this kit so can't say whether
it's "well done" either.