Rethinking this issue:
Miles and Dez are insane physical athletes and when both are healthy and used right, they should rip through defenses. Witten is essentially the 1st, 2nd, or 3rd WR in every game so the need to find a 3rd WR is not as urgent. So there is a luxury that Dallas can allow some of the talent to develop and not have to dump off the raw players (like they do at CB) in favor of experienced players.
So that leads to Andre Holmes. 6' 4" 200 and runs a 4.42. Looking at his Division II stats and taking them with a grain of salt, it seems that he is capable of being a reliable target. The number of yards (1300+) is okay but his 104 receptions in a season shows that he can be a workhorse. It is logical to think that he was the number 1 passing option on the team and the opposing defenses probably schemed to stop him.
All that to say that with Ogletree (if he makes the team), and then the development of Harris and Holmes, the WRs really do not need much attention. Aside from maybe a PR/KR type player, which would have to be better than Harris, the Cowboys can essentially just wait for UDFAs or be patient with the waiver wire.