While it is a pre-fabricated part, i believe it falls under the category of R04-C:
"COTS parts and assemblies may only have a maximum of a single degree of freedom. It is the intent of FIRST that teams design and build their devices to achieve the game challenge. Assemblies of COTS components, such
as
linear slides, and gearboxes are allowed "
It would be considered a linear slide, and would probably be allowed. My team uses these
http://www.homedepot.com/p/Liberty-1...ZP-W/202200643
Similar purpose, but they are cheaper. Good luck!