Ubisoft hasn't verified such an event is coming however, so speculation and leaked images are that from until an official confirmation is R6 Credits provided, gamers need to go.
Until an event is supported, if it be occurring, Rainbow Six Siege players have the game's latest patch to play on and hold them until Halloween comes around. More upgrades are expected to come before then, but Ubisoft's newest most recent changelist made some sweeping changes to teamkilling that individuals who grow frustrated with their teammates may want to take note of.
"The group killing punishment for a first offense will be adjusted from a kick into a 30 minute prohibit," Ubisoft's patch notes said with a full breakdown of their new teamkilling penalties found here. "Initially, if a participant was team murdered in Casual, the offender was kicked from the match. The identical situation in Ranked could result in buy Rainbow Six Siege Credits a kick as well, but also triggered an abandon penalty. This was perplexing because it appeared as if the team killing punishment was distinct between Ranked vs Casual."
Looks like Halloween is coming to Rainbow Six Siege at a big way. A brand new playlist teasing a version of the home map redecorated for Halloween appeared following the most recent patch on the menu. It disappeared like a ghost -- or like a Ubisoft engineer realizing a new holiday feature had been revealed.