Thanks for the pointer to the OWL info.
From the page you reference, a leader "should" have OWL, but it doesn't say that he/she "must" have OWL for Webelos den camping. So, OWL not absolutely required according to the wording.
However, a Local Tour Permit may be required depending on location, distance, etc. Even in this case, though, the BALOO requirement on the Local Tour Permit application does not need to be satisfied since BALOO is for "pack" overnighters, not den overnighters.
So, neither BALOO nor OWL is absolutely mandated for Webelos den camping.
Do I understand the forms and requirements correctly?