In general, evocation is concerned with relatively brute-force, straight-line manipulation of various types of energy. Manipulation of luck is outside of that, so it wouldn't normally be something you could do with evocation.
It depends on what you consider a straight line of manipulation. Water is the element of entropy and as such can be justified for creating effects that lead to decay by increasing chances or the probability of something breaking or entropy being held off and used for protection. How can that be modeled in the combat options of evocation? Pretty easily.
Other elements can be justified for probability manipulation in much the same way with a little creative thinking.
The main thing will be to create narrative justification for it, which really isn't that hard.
The things you'll be able to do to manipulate probability or luck or entropy or whatever will be fairly straightforward and simplistic though, since you only have the four options of attack, block, counter spell and maneuver. The effects will also be short lived, because hey it's evocation. For more complex or longer lasting effects then yeah, Thaumaturgy will be what you're going to use.
Personally I don't see anything wrong with the caster who wants to use a touch of subtlety and roll a spell to alter the roll of some dice at a casino. Maybe a maneuver to create an Aspect that can be used in a social conflict by fate giving him the hint about what's the right thing to say. Cast a block that changes the "chances" of being hit offensively in combat or any number of applications.