Not a simple yes or no answer, because once installed it will depend upon how much the locker is used. When not engaged it adds no stress, when it is engaged it increases stress on gears, shafts & housing, often significantly depending upon the situation. An automatic ;ocker like a Detroit is going to be harder on things than a selectable locker like an ARB, simply because the Detroit is essentially always engaged. It's a sound idea to upgrade axle shaft strength (material & spline count) and use a good quality gear set when upgrading to a locker.
'09 JKRU. 4" Teraflex long arm, Teraflex R44 housing, Teraflex / Fox Resis, Poly Performance skids, Nemesis Billy Rockers, Nemesis flares, 37" ATZ P3s on 17" 5x5.5" Trailready HDs, Spyntec hubs, Teraflex BBK, Mopar BBK master/booster, Superior front & Alloy USA rear axle shafts, CTMs, Reids, Synergy drag link & tie rod, WTOR hydro-boosted steering, 5.38s, TF Dual Rate front bar, TF bumpers, Warn Powerplant, Tom Woods shafts, AA xfer case cable, Kilby canister relo, RH4x4 cage.