The Boyzone star, who sits on the Australian panel alongside the Spice Girl, was surprised by the audience reaction to her guest spot on the UK version.
"She's just honest and we love that about Mel. And that's why she should be on the panel. You need those sort of comments," Keating told Heat.
"I know Mel pretty well and she's never shocked me. It'd be boring if all of us were the same."
Scary Spice was nicknamed "Grumpy Spice" by Gary Barlow, Louis Walsh and Tulisa Contostavlos on Saturday's (August 18) show after she criticised most contestants.
After she told an 82-year-old man who sang Adele's 'Make You Feel My Love' that she "actually wanted to fall asleep", host Dermot O'Leary asked: "Where is her heart?"
X Factor UK producers reportedly want Mel B for the 2013 series following her controversial guest stint.
Watch Mel B on The X Factor UK below: