Yes, the bootloader is locked on the Nexus 7. Don’t worry, you can unlock it. Follow these simple directions:
First, you need to put it in USB debugging mode. Next, you need to make sure you have the Android SDK installed on your computer. Finally, you need to use the fastboot oem unlock command.
We recommend you unlock it before loading all your data and apps on it as unlocking the bootloader will wipe the device.
Source: Android Central