Whether it should be italicized or not is a matter of the style guide you follow.
While I can't find ad hocness in Merriam-Webster, it is in Oxford—and both list ad hoc.
In all of these cases, the dictionaries show them in roman. (I only used italics for emphasis.)
So, barring something I wouldn't expect from a style guide, I would say that it should remain in roman. (Normally, style guides say to follow your main dictionary.)
Both dictionaries also define ad hoc (and Oxford, ad hocness) in an open form.
For hyphenation involving an open-form term, you would not normally add a hyphen to the term itself. So how would you deal with your example?
One possibility is mentioned by The Chicago Manual of Style (17th ed.), 6.80:
The en dash can be used in place of a hyphen in a compound adjective when one of its elements consists of an open compound or when both elements consist of hyphenated compounds . . . Whereas a hyphen joins exactly two words, the en dash is intended to signal a link across more than two. Because this editorial nicety will almost certainly go unnoticed by the majority of readers, it should be used sparingly, when a more elegant solution is unavailable. As the first two examples illustrate, the distinction is most helpful with proper compounds, whose limits are made clear within the larger context by capitalization. The relationship in the third example depends to some small degree on an en dash that many readers will perceive as a hyphen connecting music and influenced. The relationships in the fourth example are less awkwardly conveyed with a comma.
the post–World War II years
Chuck Berry–style lyrics
country music–influenced lyrics (or lyrics influenced by country music)
a quasi-public–quasi-judicial body (or, better, a quasi-public, quasi-judicial body)
If following this guidance, you might use:
Careful readers might notice its distinction from the hyphenated form:
But if the en dash version doesn't work (or even the singly-hyphenated form), then the only option to avoid awkwardness is to rephrase it.
You would need to use something like what you originally wrote:
. . . its lack of ad hocness . . .