Almost every relevant stat can be seen by using the Mind Read spell, including lust. Why is lust excluded from the basic interface? I don't know, maybe there wasn't enough space or maybe it wasn't considered to be important. Lust has limited impact on gameplay.
If a slave has moderately high lust, then there is a weak debuff. If a slave has very high lust then there is a less weak debuff. Either way it is unlikely to significantly impede your combat abilities past about level 4.