Who are "Holelim"?
Rashi: They are those who mix their ways. This is like "Sav'ech Mahul ba'Mayim" (Yeshayah 1:22).
Radak: They are Resha'im. They engage in pleasures and lusts of this world, which is folly. They are not concerned if they rob, steal or do any evil to fulfill their desire.
Why was he jealous of Holelim?
Radak: I saw them b'Shalom - therefore I was jealous until my feet almost veered!
Malbim: They succeed in this world. There are three ways in which they are unlike others. The masses of people are prepared for three general evils. (a) Due to the composition of their body, which is soft and weak. Man's nature is prone to cease and lack, via constant decrease of fluid until death. This does not affect Resha'im! Also refer to 73:5:1:2, 73:5:2:2.