The rack needs to be solidly mounted and should not move. It is definitely not a good thing if you are seeing this type of play. The steering rack bushings on basically all Sequoias and Tundras are well known for this problem.
Good news is that there's a company out there that makes new bushings for these out of polyurethane, which is a material that's far stiffer than rubber. These bushings are meant to prevent the rack from being able to move side to side like that.
Energy Suspension part # 8.10104
Just read the reviews on this page:
8.10104 | Rack and Pinion Bushings | 00-06 Tundra 01-07 Sequoia