Is it correct to say "in wild" instead of "in the wild" (= in natural conditions)?
I've updated my initial question: is it possible to use "in wild" in titles, as in this article?
No, you cannot use the phrase in wild to mean in the wild.
However, as with many things in English, there's an exception: headlines. In headlines, several grammatical conventions are often ignored. Among other things, headlines generally drop "little words", like articles and certain forms of the verb be, in order to save space and make the title catchier. Some headlines even replace the word and with a comma. That means you may see headlines like the one you linked:
Newly discovered ruby sea dragon seen alive in wild for 1st time
In normal usage, that sentence would have to be something like:
A newly discovered ruby sea dragon was seen alive in the wild for the 1st time.
With regards to the in wild vs in the wild distinction, you can see that, in the body of the article, the authors use in the wild, because the body isn't a headline.
However, the video showed that, in the wild, their tails are actually curled.
As The New York Times Manual of Style and Usage puts it*:
To save space, the verb to be (in forms like is, are, was, etc.) can be omitted, but only from the first phrase of a headline ... And if any "little words" (verbs or articles) must be omitted for space, drop the leftmost ones first.
Additionally, headlines uses tenses differently than you might expect. To quote from the NYT again:
Headlines on fresh news almost always use the present tense: Men Walk on Moon. If the headline relates a current action to an earlier one, drop back only one level in time, to the past tense: Governor Signs Bill She Opposed (not the past perfect Had Opposed). When recalling history or newly disclosing a past development, also use the past tense: Miel Left Millions to College.
One more quirk of headlines (actually, for this one, of titles in general) is the usage of capitalization: in American English, it's very common to capitalize every word (other than "little words" - the precise definition of which varies) in a title: Firefighters Rescue Cat and Dog From Tree (or Firefighters Rescue Cat and Dog from Tree, depending on your style guide) , but in many other forms of English, only the first word of a title and any proper nouns are capitalized: Firefighters rescue cat and dog from tree. You can see examples of the American usage in the NYT's guide, and of the non-American usage in the article you linked, from the Canadian CBC.
* The NYT style guide is by no means the only opinion on the matter, particularly outside the US, but it's a widely respected one.