If I remember correctly, when WDEL was carrying Hannity, he was prempted for the Phillies (I'm assuming the Phillies contract required they be aired and other programming prempted), so I'm not sure why WDOV wouldn't have that sort of agreement with the Blue Rocks, but maybe Minor League teams don't have that sort of clout. However, when ABC radio tried to force WDEL to take Levin in order to keep Hannity maybe the contract was going to be changed where WDEL would have to prempt the Phillies rather than Hannity and that might have been a deal breaker for WDEL who's carried the Phils for years and seems to have a heavy spot load for each game broadcast that I've heard.
Chris Carl from WDEL usually reads these posts so maybe he can offer some insight into how Hannity's contracts work.
Another consideration for WDOV prempting the Blue Rocks game rather than Hannity, maybe WDOV was able to sell Hannity better than the Blue Rocks and decided to give that the preference as they had actual paying customers buying time for Hannity and none for the Blue Rocks. I noticed the other night that WILM had no spots for several spot breaks of the Blue Rocks game I listened to (they aired PSA's like they do during Rush).