Soo I cooked up a beta version that'll probably fix your issue:
https://s3.eu-central-1.amazonaws.com/nb-stor/dos/ExportTool/ExportTool-v1.8.7-beta.zip

After importing the original .GR2, you should check the "Copy skeleton from:" checkbox and select the source mesh that contains the skeleton that is being animated. For example, when exporting "Creatures_Dragon_ABC_Attack_UA_01.GR2" you would use "Creatures_Dragons_A.GR2" as a skeleton source.