Like his predecessor Notker, Ymmo was regarded as a gentle abbot. However, he is also described as a strict follower of the Rule of Saint Benedict. Ymmo succeeded in initiating an economic revival for the abbey and also managed to recover or acquire new property. The Church treasure accreted under his rule, wherefore he was able to let new frescos be painted in the churches of Gallus and Othmar. Furthermore, he built the chapel for the holy grave with a crypt dedicated to Saint Ulrich.