I've never heard of either drug being contraindicated in the low doses used for sleep. Its true that higher doses have the potential to cause serotonin syndrome but they are quite commonly prescribed with other antidepressants. My roommate was on 40mg of citalopram, 150mg of trazodone, and 300mg of bupropion XL and when you go inpatient at psych hospitals, they always dole out either trazodone or mirtazapine for sleep to pretty much everyone unless they have an allergy to them. When I went to the psych hospital they gave me 200mg of trazodone in combination with my 150mg of lamotrigine and 20mg of citalopram without a second thought.
It is worth talking to a doctor about, they're a godsend for people who can't sleep otherwise.