The Gemara in Berachot 42a quotes Rav Yehuda, who holds that “pat haba`a bikisnin” requires the beracha of mezonot, and not that of “hamotzi”. The Shulchan Aruch (Orach Chayim 168,6) brings this as the halacha as well.
As to what exactly constitutes “pat haba`a bikisnin”, the Rishonim bring different definitions: dough mixed with honey (Rambam), dough filled with honey and almonds (Tur), or dried baked goods like pretzels (Rav Hai Gaon). The Shulchan Aruch (ibid, 7) rules that one should say mezonot over all of these; perhaps he understood that the opinions merely reflect different applications of the halacha, but don`t necessarily disagree.
What about sweet rolls (“mezonos” rolls) commonly served at simchas? Can one indeed recite mezonot on them?
The Shulchan Aruch writes that mezonot is said as long as the dough was mixed with honey. However the Rama disagrees, and requires that there be a significant amount of honey in the dough; mere taste is not enough.
Therefore it would seem that the Rama would require hamotzi for “mezonos” rolls, as the sugar component is not great in them, whereas the Shulchan Aruch would suffice with mezonot.
However, even according to the Shulchan Aruch it would seem that in fact hamotzi would be required for “mezonos” rolls, because anything which one establishes a meal over requires hamotzi – and certainly one is basing himself on these rolls at the meal.
Even if one would eat only a little of the “mezonos” roll, and would fill up on other things (meat, fish), nevertheless the Mishna Berura (ibid, 24) quotes the Magen Avraham who holds that that extra amount of food combines with the “pat haba`a bikisnin” being eaten to form an amount that most people would consider sufficient for a meal.
Therefore it would seem that the correct practice would indeed be to wash and bench over “mezonos” rolls served at simchas.