Do you mean electrically "fault free?" VHDL is a programming language, not a test instrument. If you want to verify that the inputs respond to the appropriate levels, and the outputs deliver the appropriate levels, speed etc, you're going to need some instrumentation.
i think if the output ports are assigned to some input pins in that case chipscope can track them, I'v done this to verify the signals on Ethernet phy layer chip,
if you want to verify all by software then I think chipscope is the way to go, otherwise you need logic analyzer to verify signals.
The OP asked if you can use VHDL to verify the output levels of an FPGA. The answer is no. Somehow, this devolved into an argument about chipscope. If you want to analyze the outputs of a device, you will need an oscilloscope, a data acquisition system or similar. And you cant measure rise time and voltage levels with a logic analyzer.