Using the most recent tweet from Mike Marts, and looking at the tweets from the artists associated, we can deduce the (three) artists working on Batman and Robin # 16, before DC makes any such official announcement.
Cameron Stewart is solicited for the art duties. Those who follow comic news from conventions and twitter as well as the main news sites already knew that Stewart wasn't going to be completing the entire issue, that he would have some help. He had mentioned Frazer Irving to a few people at conventions, which has now been confirmed from the aforementioned tweet from Mike Marts, as well as additional pages drawn by Chris Burnham, artist on Joe Casey's Officer Downe from Image.
The tweets, from Marts, and another from Burnham, are found here and here, respectively.
From Marts, earlier this morning:
"Batman&Robin 16 off to printer! Big thanks to @grantmorrison @javisoperandu @TheBurnham @cameronMstewart @gimpnelly PatBrosseau n AlexSinc!"
(javisopeandu is Frazer Irving's twitter, of course TheBurnham is Chris Burnham's and cameronMstewart is Cameron Stewart, the art team on the issue. gimpnelly is Jenelle Seigel, one of the editors on the title, PatBrosseau is the letterer, Pat Brosseau, and AlexSinc is Alex Sinclair, the colorist for, most likely, Stewart and Burnham's pages as Irving does his own colors customarily)
From Burnham, one week ago today:
"... I've got 7 pages in Batman & Robin #16!!! Grant's last issue on the series! On sale Nov 3rd! 6:31 PM Oct 14th via web"
Anywho, I knew that Irving was helping out, but now we've got the entire creative team laid out for us.
Edit: I began this post before this was posted, but didn't get to submit it until afterward. Mods, perhaps you could move this one over there?