A Daniel Whitehall cameo in Agents of SHIELD touched upon Hydra, Ghost Rider, Life Model Decoys, and plenty more Marvel hallmarks besides. Though Agents of SHIELD suffered no lack of top-level villains, Daniel Whitehall (later revealed as Hydra's Werner Reinhardt) was arguably the best of the baddies. Played by Reed Diamond, Whitehall worked under Red Skull, but was captured by SHIELD after World War II and given a stern interrogation by one Peggy Carter. Whitehall returned to prominence in the modern day, where he led Hydra and continued to pursue his previous experiments into Inhumans.
There's no question Daniel Whitehall stands among Captain America: The Winter Soldier both became running plot points, while the likes of Nick Fury (Samuel L. Jackson) and Lady Sif (Jaimie Alexander) made cameo appearances.
While Agents of SHIELD's early seasons drew plenty of connections to MCU movies, the affection wasn't exactly reciprocated. Agents of SHIELD's only representation on the big screen has been Clark Gregg's Phil Coulson, but even then, there's precious little crossover. Intriguingly, 2019's Avengers: Endgame came close to breaking that trend. Unused visual effects shots (via BEJT_T on Twitter) designed for the scene where the Avengers plan their #TimeHeist would've included photographs of Hugo Weaving's Red Skull, Toby Jones' Arnim Zola... and Reed Diamond's Daniel Whitehall. Since Whitehall would've been in SHIELD custody during Tony Stark and Steve Rogers' trip to the 1970s, a live-action appearance could've also been possible (although he was kept at The Rat, rather than Camp Lehigh), and Diamond responded to the images with a tongue-in-cheek comment about Marvel checking his availability, suggesting he would've been interested.
Avengers: Infinity War into its narrative, and by Agents of SHIELD season 6, direct references to MCU events had dried up, turning into more general Marvel nods instead. Agents of SHIELD happily did its own thing from there, relying on awesome character chemistry and quirky humor than teasing links to the MCU.
When Avengers: Endgame released in 2019, Agents of SHIELD was an entity unto itself, enjoying the freedom and independence MCU separation brought. Had the Avengers' time heist name-checked Daniel Whitehall, Agents of SHIELD's canon status would've been thrown into turmoil all over again, muddling a final run of episodes that were largely MCU-free. If Marvel movies wanted to acknowledge Agents of SHIELD, 2013-2017 was the time to do so, not 2019 when Coulson and the gang had already pretty much gone solo.
That's not to say a Daniel Whitehall cameo in Avengers: Endgame couldn't be plausibly explained. Though Agents of SHIELD's relationship to the MCU remains ambiguous, the safest assumption is that the TV timeline takes place in a different universe, where Earth history was more or less identical to the prime reality up until 2012, before splintering off. As such, the MCU would have its own version of Whitehall, explaining his photo sitting alongside Red Skull and Zola on SHIELD's records. Still, avoiding the debate altogether was probably the safer bet.
