What happens if you add it to the file like that?
It's been a while but I think you need to add it to the qclocations file anyway, otherwise you can't pick the airfield in QC. Also, I believe the name you use in the cutscenes.xml should match the facility file's name. But again, it's been some time since I played with airfields...
Frosty
BTW, there's a typo in your entry - maybe that's the problem:
<TOW_Deelen_airbase>
<Cutscene FileName="g_pregame_2.xml"/>
</TOW_Deelen_airbase>
Note the forward slash in the last string! If you edit the file in an XML editor or view it in Explorer, I think it might give an error on opening or closing of the file, pointing you to the faulty string.
You can always copy an existing and working entry and change the contents to suit your files.