Firstly, not being able to release in-house tools is a complete non-issue.
Secondly, if the programs are loosely coupled, the GPL, especially GPLv2, is very forgiving of proprietary code and GPLed code working together. You just have to mind your manners and know the rules. For the GPLv3, here are some basic rules from the GPL FAQ:
For instance, if the program uses only simple fork and exec to invoke and communicate with plug-ins, then the plug-ins are separate programs, so the license of the plug-in makes no requirements about the main program.
If the program dynamically links plug-ins, but the communication between them is limited to invoking the ‘main’ function of the plug-in with some options and waiting for it to return, that is a borderline case.
Furthermore, the system library exception may prove useful sometimes as well, though that is less common.
In conclusion then, while there is a kernel of truth hiding very, very well around what you are saying, it is largely FUD. From the GPL FAQ again:
Which programs you used to edit the source code, or to compile it, or study it, or record it, usually makes no difference for issues concerning the licensing of that source code.
Finally, although far less importantly, if you suppose that the GPL is violated by your project in some subtle manner (just don't copy code, mkay?), chances are, it doesn't matter unless you are doing something particularly malign. In general, someone else will have to find some way to prove you violated the terms of the license. Furthermore, generally organizations like the FSF provide an ample chance to fix noncompliance, even deliberate noncompliance. I highly doubt there is a recorded case of someone being made sorry for using the GPL in good faith.