I've recruited a D3 freshman with 1 WE, and it worked out fine. Guy came in with high 70s perimeter, and I needed a shooter off the bench. He had adequate defense, and even wound up starting a number of games his senior year once his IQs rose to around the A-/A level. You just have to know going in that the lower the WE, the more you have to be comfortable looking at the player as he is now and essentially ignoring the potential. But I certainly think all the coaches who say, "I won't recruit any freshman with a WE less than x" are just shooting themselves in the foot. There aren't a lot of guys out there you want to play at D2/D3 with their initial ratings, but keep in mind that WE does carry some weight in the calculation of where players think they belong, so a D3 recruit with very low WE is likely to be at least a slightly better starting player, on average, than a D3 recruit with very high WE. I just don't see why anyone would ever basically rule out 15-20% of all recruits without honestly weighing them against their higher-WE competition.
Depending on your system, you play undergraduates anywhere from a decent amount to quite a bit on an average team. Sure, the high WE player is going to be better their senior year, probably by the end of their junior year. But that means that for the first 2+ seasons, and the first 2 postseasons, the low WE player is more valuable. If your team is good right away, and the low-WE guy fills a need, he might well be the better choice. If you're a cream-of-the-crop coach and you're going, say, E8 or better every season, maybe you never throw a roster spot to a low-WE guy. But otherwise, if he helps you compete in your more competitive seasons, sometimes you have to go for it. And let's be honest, there's so little competition for low-WE players they're cheap as dirt. If it's a choice between a second walk-on and a low-WE shooter or rebounder, go for the player, even if you are a top-tier coach.