I don't know the part, but a sample usually has a sound of it's own. That's usually the reason people are using them.
It is just a distorted guitar riff that repeats on an infinite loop, not many notes really, totally understandable that they used a sample instead of someone playing that.
Except for the fact that if you have someone play it, it will actually sound, you know, LIVE 
I don't give a s*** to have someone playing that filling riff live, I actually don't like it at all!
I think the problem with this riff, which are many, is as follows: 1) You need an extra electric guitar in an open tuning to play it; 2) It's kind of tricky to play as it requires some fingerpicking, not simply strumming; 3) Not only that, it also has a wah-wah effect, gotta think about it as well; 4) As it's so prominent and recognisable in the song, the slightest mistake will stick out like a sore thumb, so better to play it perfectly each time.
So not only do you need to bring an extra guitar and pedal just for this riff and somebody skilled to play it, but it has to be good too. So you either take it out of the arrangement completely, like something Mark did in the early DS or just ask Guy to play a sample, it's so much easier. Overall, a great solution for this particular song. Hats off here, no critique at all. A perfect solution to a problem that not many people would even notice.