Legal parts

I wonder if the parts from the Field Element kit are legal for a robot.
One of my teams used the spare double-wide 2x3 corner connectors (228-3201-137) that are really useful, but only available as part of the field elements.
And if they are legal, where can I get more of those without buying a bunch of Bank Shot Fence Kits (now the other teams are like: “More, more!”)
Out of curiosity (with no planned application) and going little extreme, would the pipes be legal too?

The connectors are legal for use on a Robot. The pipes are not. The connectors are not currently available as individual parts, however you may find some in various VEX Robotics by HEXBUG kits.