Have there been any notable collaborations or crossover events within the DC Universe Card series that involve popular characters or story arcs?

Yes, the DC Universe Card series has featured notable collaborations and crossover events that highlight popular characters and significant story arcs from DC Comics. One prominent example is the Hro x DC Events Collection, an 18-card hybrid set that showcases major crossover events from "Crisis on Infinite Earths" (1985) to "Dark Nights: Death Metal" (2021). 

Additionally, the DC vs. Marvel crossover event from 1996, which pitted iconic heroes from both universes against each other, was commemorated through trading cards. SkyBox released a series of 100 base cards expanding on the battles featured in the miniseries, praised for their high-standard artwork. 

These collaborations within the DC Universe Card series not only celebrate pivotal moments in comic book history but also offer collectors a tangible connection to these landmark events.