You should be able to do something like this:
MailChimpManager mc = new MailChimpManager(** apikey **);
var emails = new List<EmailParameter>();
emails.Add(new EmailParameter() { Email = ** youremail ** });
var info = mc.GetMemberInfo(** listid **, emails);
var member = info.Data.SingleOrDefault();
if (member.Status == "subscribed") {
** email is subscribed **
}
else {
** email is not subscribed **
}