To play two player split screen on horde at least (idk about online other modes) each person needs an active Xbox live account.
The way i do it is sign up for a free month of Xbox LIVE gold account, all u need to do is go to xbox.com, after making up some fake email account, and you can have a free month of xbox live. Takes like 10 minutes tops to do.
But yes Horde is splitscreen co-op online