Is it usual to use “full-cry” as a stand-alone adjective?
The OED has an entry for full cry that may be more useful than those you’ve found. It is sense 12b. I will give the a sense, then the b sense with citations:
12. a. The yelping of hounds in the chase.
b. Hence various phrases: e.g. to give cry, to open upon the cry; full cry, full pursuit; also fig.
- 1589 R. Harvey Pl. Perc. 6 ― Will you··run vpon a Christen body, with full cry and open mouth?
- 1649 Fuller Just Man’s Fun. 13 ― Hear the whole kennel of Atheists come in with a full crie.
- 1684 R. H. Sch. Recreat. 16 ― Being in full Cry and main Chase, comfort and cheer them with Horn and Voice.
- 1710 Palmer Proverbs 53 ― He gives out this cue to his admirers, who are sure to open upon the cry ’till they are hoarse again.
- 1858 Hawthorne Fr. & It. Jrnls. II. 32 ― All offering their merchandise at full cry.
- 1891 Rev. of Reviews July 25 ― The journalists gave cry after the Prince, like a pack of hounds when they strike the trail of a fox.
So it appears that the phrase is quite old. It seems to mean “full pursuit”.
Interestingly, the very oldest citation for the word cry is a citation from Laȝamon that ends in “doleful cry”:
- C. 1275 Lay. 11991 ― Nas neuere no man··þat i-horde þane cri [C. 1205 þesne weop] hou hii gradde to þan halwes, þat his heorte ne mihte beo sori for þane deolfulle cri.
That is a “doleful cry”, so one of pain, a dolorous one. It doesn’t actually mean in full cry there.
"Full-cry" is not a stand-alone adjective in the phrase "full-cry pursuit"; it's part of a larger noun phrase: "full-cry pursuit". The general rule about using two words to modify a third is that the first two words are hyphenated, as is the case with "well known" (ADV+ADJ) when they're in front of the word they modify, e.g., "He's a well-known liar", but isn't hyphenated when they appear as a predicate adjective phrase, e.g., "That he's a liar is well known". This is the case with "full cry/full-cry". "In full cry" is a prepositional phrase with a noun phrase, "full cry", as the object. "Full" is the adjective, "cry" is the noun, and because the PP's a complement that isn't modifying an immediately following noun or noun phrase, it's not hyphenated. There are many such collocations that don't appear in the dictionary because the rule that we follow is clear and simple (if writers can remember it and care about following such "rules").
To answer the basic question, it does not seem to be usual. There is only one record of its use in the Corpus of Contemporary American and English and none in the British National Corpus. The fact that it is unusual does not, of course, mean that it shouldn’t be used.