There have been no modifications to any of the packages used, no adware, trojans, toolbars, etc. This is simply a tool to help people get around censorship."
I have no reason to believe that it contains any viruses, but if it did, they'd obviously say the same thing.
The bigger issue is making build environments reproducible such that it's possible to arrive the same binaries deterministically, and therefore proving that there's nothing outside of the code. It's possible, but it's tricky, especially with stack randomization and the other minutia of slightly different configs. More apps like the opensuse build service, brew bot and travis might help.
For the osx client, I built bitcoin-qt from source with openssl 1.0.1f.