I don't think any credible vulnerability researcher would conclude any of those companies' software vulnerabilities were back doors. If you know of one, please let me know.

All of these companies write software in languages that require the programmer to track memory management and bound their own copies. The probability that software written in languages like that will generate a memory corruption vulnerability is extremely high.

Has Juniper actually been damaged by the backdoored source code scandal (which is the only genuinely back doored American company I can think of)?

This report claims a 5% YoY net revenue increase, along with higher GAAP profit. http://investor.juniper.net/investor-relations/press-release...