Obviously, students who learn how to touch type have the advantage of being able to type faster. If the touch typist cannot articulate what it is that they need to type, then this advantage will do them no good. If two students have equal skill in computer programming, but only one knows how to touch type, then it follows that the touch typing student should be able to complete tests and assignments faster.
However, there some good reasons not to make it a required prerequisite.
As has been noted in other answers, touch typing is a skill that is advantageous, but not necessary. It seems to me at least that it is very possible to be a decent programmer without knowing touch typing...
My school required me to take a basic computer class, and one of the promises of that class was that it would teach touch typing. I wanted to learn touch typing in that class. It did not happen. I was not taught how to touch type. I was passed without ever being tested on touch typing (which is a bit sad). Any of the hunt-and-peckers in that class would have technically cleared a touch-typing prerequisite.
With the quality of any of the typing classes I have seen, making sure students are up to speed on typing by requiring a prerequisite course would be a hit-or-miss effort. If you are really confident in the quality of your school's typing classes, and typing at around 60wpm is really necessary (and cannot be compensated for by other things, which I doubt), then you have a slightly better case. If you really want students' grades and pass rates in your class to correlate with their speed, you could alternatively try having assignments and tests with stricter time limits, and encourage the students struggling with those limits to learn touch typing, but I don't recommend this; I would be careful not to prioritize typing speed so much that it interferes with critically thinking and writing quality, efficient code.
I still do not know how to touch type, and I would still like to learn, as it has clear advantages. I am sure touch typing could improve my typing speed by 30-60%, or by about 15-25 words per minute, possibly faster if I was really dedicated and learned Dvorak or Colemak.
However, without any training, I type with four fingers on each hand (not the pinky fingers) at about 45 wpm. I know the keyboard well enough to type without looking. Stopping to think about something for a minute is far more likely to slow my typing than me not being able to type fast enough. I do not see a pressing need for a typist similar to myself to learn touch typing.
In my computer science classes, I am sure that many of my classmates have the ability to type faster than me. However, I am often the first one done with assignments and timed tasks, as I can think of an efficient solution the fastest. One of my classmates used an iPad to type his code. It makes me cringe (possibly similar to how touch typists would cringe at non touch typists like myself), but he managed a surprising amount of speed by adding and using IDE shortcuts.
My employer did not look at my typing speed when they hired me. However, I can accomplish certain tasks far faster than others would, because I use scripts, macros, and other shortcuts that most would not consider.
My grandmother learned how to touch type. She can type probably twice as fast as me. But that is not the same thing knowing how to efficiently use a computer and all the shortcuts that are now available with it.
Have students who are blazing fast touch typists? Good for them. The rest (non touch typists) will probably either learn to compensate well enough or possibly fail. Or they may take up touch typing if they see it as necessary enough, especially if you encourage them to do so.