In a very nice quality of life update, it appears that most, if not all, raid skips are now account-wide in Patch 11.0.5! As far back as Warlords of Draenor, all raid skip quests now have a note that they were previously completed by a character within your Warband, allowing all other characters to use them.
Courtesy of MrGM
This is a great change for collectors, as they can now much more easily use alts to skip to later bosses that typically drop cosmetics, mounts, and other highly desired items. Keep in mind that quest progression is not account-wide, though.