Are there canon or otherwise widely accepted names for groups of Starcraft 2 units?

Solution 1:

No, there exist no such collective nouns (or terms of venery) for SC2 species. These sorts of terms in English are completely superfluous and have no practical usage in modern day. As such, many of these modern day terms are simply made up for entertainment. From the Oxford Dictionary page on the topic (emphasis mine):

Many of the following terms belong to 15th-century lists of 'proper terms', such as those in the Book of St Albans attributed to Dame Juliana Barnes (1486). Some are fanciful or humorous terms which probably never had any real currency, but have been taken up by antiquarian writers, notably Joseph Strutt in Sports and Pastimes of England (1801).

Why does that matter when it comes to Starcraft? Easy, these terms are not used in everyday contexts and are more "trivia" then actual content. Books containing stories of war and drama and chaos don't often interlude with "Fun fact: did you know a group of zerglings is called a gang?"

In universe, because these terms come from hunting, you don't think of people as "hunting" Hydralisks. Nor would people go out for a day of shooting Zealots in waders with a Zealot caller. There would be no reason that these terms would have ever been invented within the context of the war against these races.

Out of universe, the fans are less concerned with terms meant for hunting, and more concerned with strategic groupings. It is more useful to have the term "Speedlings" than "a zeal of zerglings". Any reason to invent the terms would be done purely as a way to invent trivia for the game. And the invention of terms would likely be difficult to propagate because of any conflicting naming and lack of utility in conversation by hardcore fans.