From the grammatical point of view both usages are perfectly correct. So, your question is not about grammar but about style.
In a nutshell:
You use a word that already is rare not as it is used normally, but in a rare manner. And this is why both sentences sound a little bit odd. (But they are still both grammatically correct.)
Let's talk about grammar first:
Adjectives can be used in three different ways:
attributive (as a left attribute of another word):
As an attribute the adjective lives together with the referred word inside the same nominal group. (This is why here are only nominal groups shown. A full sentence also has a verb and often also some objects, for example: »Die schöne Blume blüht.« or »Das schnelle Auto gehört dem Sohn des Mannes, der jeden Donnerstag bei unseren Nachbarn den Rasen mäht.«)
- attribute of a noun:
die schöne Blume, das schnelle Auto, das kranke Kind
- attribute of a participle:
der ruhig fließende Fluss, die grün schimmernde Oberfläche
- attribute of another adjective:
die schön roten Mohnblumen, das unglaublich schnelle Auto
predicative (as part of the Prädikat1):
In predicative usage the adjective is bound to the subject (which often is a nominal group), and the glue is a copula. A copula is a verb like sein ("to be"), bleiben ("to stay") or werden ("to become") which doesn't describe an action but some kid of equality. In German also some other verbs (wirken, erscheinen, ...) can sometimes behave like copulas, while some other copulas (heißen) can't glue adjectives to subjects (heißen is a copula for names only).
Die Blume bleibt schön. Das Auto ist schnell. Das Kind wird krank.
adverbial (describing a verb, i.e. as a right attribute of a verb)
Die Blume blüht schön. Das Auto fährt schnell.
1 In German grammar the term "Prädikat" is defined different than "predicate" is defined in English grammar. In English grammar anything but the subject belongs to the predicate, but in German only the verb and anything that is closely and directly connected with it belongs to the predicate. So all objects of a sentence belong to the predicate in English grammar, but in German grammar they are not part of the predicate.
You can use höhnisch in all three ways:
Das ist eine höhnische Aussage.
That's a scornful statement.
Diese Bemerkung ist höhnisch.
This comment is derisive.
Thomas hat sich höhnisch über Susannes Kleid geäußert.
Thomas commented scoffingly about Susanne's dress.
As you see here, I used the adjective höhnisch to describe a statement, a remark or a comment, and this is the main usage of this adjective. It is mainly used to describe verbal expressions.
But you used it to describe a person:
Er ist ein höhnischer Mensch.
He is a taunting person.
Er ist höhnisch.
He is sniffy.
I'm not sure if this is the preferred usage in English, in German it's not. It is ok to use this adjective to describe a person, so there is nothing wrong about this kind of usage, but it's rare.
Among these alternative usages the adverbial kind sounds most acceptable to me (but only if the verb is a verb that describes some kind of talking), because in this case the adjective höhnisch again refers to a verbal expression:
Er spricht höhnisch.
He speaks sneeringly.
But the two other versions of using höhnisch to describe a person are rare.
Talking about rareness:
The frequency class of höhnisch is 16 (according to Institut für deutsche Sprache). This means that the most frequent German word (which is »der«) appears in German texts between 216 and 217 times more frequent than höhnisch. 216 = 65,536 and 217 = 131,072. So, you will find just one copy of höhnisch in a text where about 100.000 times the word der appears. And this means, that höhnisch is a rare word. Other adjectives with the same frequency class are: allegorisch, babylonisch, choreografisch, dialektisch, elsässisch etc.
The frequency of höhnisch was declining until 2005, but since then it became more popular again, as this Google Ngram shows:
So, you will not find this word really often in German sentences, even when it's used in its regular meaning (describing verbal expressions). But when it's used in its rare alternative meaning (describing persons) it is even rarer. And this is the reason, why both of your versions sound a little bit odd: They use a rare word in a rare meaning.