Most every team in a conference will be playing against other teams in that conference to close out the season. If the SEC was the Mason Dixon Conference this might happen on some kind of regular basis.
In the BCS era when "good" (don't need a big payout game) schedule out of conference they are looking for a beatable team and a game in which the risk of injury to contributors is low. If Northwestern expected to be a contender the ND game would have been prior to the start of conference games.
Nonetheless there are always exceptions and I attended two of them that are relevant here. In mid Nov 1987 ND and the Tide squared off at ND Stadium (a very nice weather day somewhat surprisingly) with ND beating a good AL team 37-6. Way back in mid Nov 1976 ND beat the Tide 21-18. From what I remember from media coverage this was the first game AL played on the north side of the MD Line. Even though they part of two game home and home arrangements I was somewhat baffled then and now as to why AL agreed to potentially bad weather games.
Think the history of the ND-USC series is a good model of how to set up an annual game for N S opponents. When the arrangement was made both teams knew the home team would have a big advantage (warm vs arctic weather and not have the logistical nightmare moving players by train) but it would balance out over time. This lasted until 1960 when USC told ND that earlier season games at ND would have to be rule or they would kill the arrangement (we needed the $ and lost our weather advantage).