I could think of two approaches to solve the issue:
1.) You could try to de-obfuscate the plugin, basically by patching the plugin. I would be careful here, because of the risks involved. Its sort of grey area. On one side, chances are high that you are not allowed to patch their software, on the other-side, if their behaviour changes Rhino behaviour, they likely do something illegal either… Check for .net deobfuscator.
2.) You could try to disable the ability to detect debugger, by applying an anti-debugger bypass:
Note that, you need to load your code first, otherwise it may not work.
Other than that, when people obfuscate their dll’s, they could not only trigger a false virus detection, they could ship malware without knowing it. So I would be careful with obfuscated plugins. At least unless you obfuscated them by yourself.
Hope this helps.