Even pre-1997 there were many different types of 'nids. Their backstory "overrun outnumber overwhelm" and "incorporate valuable genes from assimilated species to create new 'nids and upgrade existing 'nid species"; these were practically copy pasted when the Zerg backstory was being drawn up.
Zerg are the bastard children of the Tyranid - both have changed since their inception, albeit very little.
Similarly Terran Marines are the bastard children of the Space Marines - still a shameless ripoff imo, but less so than the Zerg/Tyranid; Space Marines were genetically engineered men/giants with extra vital organs and extended lifetimes while Terran Marines were mostly all normal sized ex-cons brainwashed/implanted so that they would serve as front line soldiers - striking difference.
I'd say Protoss could be the spiritual children of the Eldar - not a shameless ripoff tho. The Eldar battle armor head pieces resemble what the the Protoss' normal heads/faces look like. Some of their architecture is similar as well. Some similarities, but not a copy/paste job like the previous 2.
Then there is the whole business that Warcraft 1 was originally to be a Warhammer game spotlighting the Humans facing off against Orcs...
then again, both GW and Blizzard don't talk about that openly...