Ob walking means running 2 technicians at the obelisk from the tunnel on field. 1 will die, the other will make it in. For balance, GDI could 2 man ref hop on regular ren, but Ren-X doesn't have that. It was a fun part of Ren that should be brought back. (btw, ref hop = 1 player could jump on the back of another, allowing 1 to jump a ledge and gain access to the back of the refinery on field)
Nod should be able to harv walk to the agt but that doesn't seem possible either.