If I understand well you want to use Deviare in your GPL compatible project and hooking into a closed source application such as Microsoft Outlook, Internet Explorer, Skype, etc? The answer is yes, you can use Deviare in this context using the GPL license, we don't think that instrumenting a closed-source application via Deviare is part of your software, even when you can complement other closed-source applications.
If I want to use it with the GPL license, that only means my own code using your library needs to have a GPL compatible license, right? I can use your library with my GPL compatible code to modify other closed-source or GPL-incompatible code, right? Just checking because some may view it as using a GPL plugin with GPL-incompatible program, which violates the GPL.