Hi.Welcome to JustAnswer. I shall try my best to assist you while you are corresponding with me.
Ambien is a sedative that is usually used as a treatment for insomnia. Where as Ativan is a sedative/hypnotic as well as an anxiolytic with a stronger and longer duration of action and more side effects reported.
Ambien is sufficient treatment for insomnia in itself and the requirement of Ativan along with Ambein is rarely needed. But you can take both together, however, it can result in a longer duration of sleep as well as a slight hang over after waking up, no drug interactions have been reported when Benzodiazepines such as Ativan are taken with Ambein though.
So, both can be used together, however, use should be discouraged.