I've been in there a few times during the EAA. As Clip4 says, the plate says use OSH ASOS. The TAA pretty much covers OSH and ATW anyhow, SBM is the wrong direction.
I flew over there on a recent trip to KOSH with an Oshkosh local. He got the weather at KOSH and didn't ever check again. So, he must have determined that they were close enough.