I will say, that if you are looking for a Cahoon test case, Hifo is probably your best test case, as a freshman his catch technique, and especially hand placement were really poor, like I can't believe he made it through HS with such poor technique.
He started the first few games, but his technique issues were so bad that he was dropped from the rotation after a few games his fr. year. He then reappeared in the rotation later in the season, and I have to say, there was noticeable improvement in his technique. He still had issues, but they were much less, at least his initial hand placement on comebacks & screens was correct, which they had been totally wrong earlier in the season (the Utah pick 6 was a prime example of his issues) I have also seen improvement this season as well with him, so while in general, I may not be totally sold on Cahoon as a great coach, as someone who knows and pays attention to WR technique, I have to say there is noticeable progress, even if the overall execution isn't where one would expect.
One technique issue that was really hard to gauge were the timing routes this year, there were lots of issues with the timing, but unless you know what the route called was, it is difficult to know if those were QB or WR issues, but I suspect there was some of each based on the reactions, and while that really has to be worked out between players with lots of reps so you aren't thinking about the timing and it just happens, I can't help but think that Cahoon should be trying to do more to fix those issues that have been prevalent the last 2 years.
I think Cahoon overall gets to many complaints from fans that don't know what the crap they are talking about, but at the same time he certainly hasn't had as a position group, the level of execution needed week to week to avoid criticism, he should own some blame.

As for RB's, I do have one major technique complaint, and that is in regards to pass protection, every backfield player not named El-Bakri, need to improve in big ways during spring-fall in pass pro with JWill leaving, I have to say, I was thoroughly disappointed by how little improvement I saw in that area and it should have been a point of emphasis based on last years performances by Canada & Hall.