It can and was used in solid flat tappet applications, the main purpose was to stop the 16 "leaks" around the body of the lifter, supplying more oil to the bottom and, and also reducing windage loss. The better way, if it's in the budget, is to have the lifter bores "trued" and bushed individually, that way they are perfectly straight, and clearance can be perfected. The lifter then receive there oil via splash from the rotating assy, and drain back in the lifter valley.