Assuming a creature's hit points with Wild Shape does not count as the "regaining" of hit points inhibited by Chill Touch
You can only regain something you've lost, so Wild Shape does not "regain" hit points. Therefore the assuming of hit points via Wild Shape is not affected by chill touch. Here's why:
The default approach to interpreting such words is to use the most ordinary, applicable sense of a word as found in a dictionary, so "regain" means (OED):
a. transitive. To gain again; (literally or metaphorically) to recover possession or use of something lost.
And some further mechanics of Wild Shape are:
When you revert to your normal form, you return to the number of hit points you had before you transformed.
So for example, suppose I have a hit point max of 30 but after an injury I am down to 15, and then I Wild Shape. Now, even though I assume the hit points of, say, a black bear with 19, I haven't thereby "regained" 4 hit points. Because as soon as I am done being a bear, I am right back to 15 again - I haven't gained back those hit points that I lost earlier, before using Wild Shape.
Finally, the sense of "assume" that would be relevant is (again OED):
assume v. a. transitive. To take upon oneself, put on (a garb, aspect, form, or character).
This is nothing like the definition of "regain," which is why the two words are not listed as synonyms, nor do they have a close relationship in WordNet (one is not a type of the other, in the way that "bear" is a type of "mammal").
So when you "assume" a creature's hit points it is not the same thing as regaining your own. And since chill touch only inhibits your regaining hit points, it does not thereby stop you from assuming the hit points of another creature.