Don't know about that lab in particular, but yes concentrated Test in that range can be safely made. I personally have run a Test blend at 600 Mg / Ml with good success.
Androx400 is a blend. Blends hold at higher concentrations so 400 isn't that much. Like Noble said, they make blends at 600. Personally I don't really like blends, but I have single ester Test U at 500 that I love