Yes, this is just a form of inversion or anastrophe that is done for style. I have almost always heard it said,
The less likely he is to agree.
I think J.R. and I were discussing something similar on a post yesterday regarding the use of "remarked he" and "said he": Why "Remarked the fish" works? Why not "The fish remarked"?. Regardless, there are many stylistic inversions that one can do in English to sound more formal or elegant as I'm sure there are stylistic constructions in other languages that are used to sound more formal or elegant:
"The basis of our governments [sic] being the opinion of the people,
the very first object should be to keep that right; and were it
left to me to decide whether we should have a government without
newspapers, or newspapers without a government, I should not hesitate
a moment to prefer the latter. But I should mean that every man should
receive those papers and be capable of reading them." Letter from Thomas Jefferson
to Edward Carrington, 16 January 1787, Paris, France.
"Should anything go wrong, call me immediately."
"John will continue to do the work, be he the last one to leave or not,
and will eventually get it done."
"She is neither happy, nor is she sad about what has happened."
In Thomas Jefferson's letter, I put sic after "governments" because Jefferson, throughout his letter to Edward Carrington, is clearly talking about the United States government and not multiple governments. What I think Jefferson meant to do is put an 's so that it read, "The basis of our government's being...," since the "of" actually opens up a gerund phrase wherein "being" is acting as though it were a noun despite its not being one technically. Anyway, I've started to digress. Jefferson also uses inversion of the simple past subjunctive "were" above, rather than stating "if it were left", which voids the "if". We see this in the following sentence with "should anything go" wherein the "should", which is being used to replace the present subjunctive, is inverted, thus voiding the "if" that would exist if it were not inverted:
"If something should go wrong" or "If something go wrong".
The same thing happens in the "be he" example wherein the "whether" is voided because of inversion.
Inversion is usually stylistic, but not always as evinced in the "neither...nor" example I've posited for you. In this example, it must be written using inversion ("nor is she) for it would be wrong were it written "nor she is". These are just the idiosyncrasies of language. I can't explain to you why such idiosyncrasies exist, but they do.
I hope that might have helped you out. Take care, Godspeed, and good luck!