Gist
Yes. Rucking can support fat loss by increasing the energy cost of walking, but body-fat reduction still requires a sustained calorie deficit.
Yes. Rucking can support weight loss because carrying external load raises the energy cost of walking, but lasting results still depend on an overall calorie deficit.
Yes. Rucking is useful for general fitness because it combines aerobic exercise, weight-bearing movement and whole-body strength-endurance, but it should complement rather than replace strength training.