Which is it-rabbits are unnatural prey that they didn't evolve to eat or adult snakes sometimes eat small rabbits? If I'm being really particular, domestic mice aren't what they "evolved to eat" either. Hispid cotton rats, eastern moles, white-footed mice, anoles, skinks, and young birds are some of the prey items they consume in different portions of their range and at different life stages. Now there's certainly no debate that sausage links of ground meat of any type aren't part of the natural diet. That doesn't necessarily mean they're bad to feed though and they certainly may be superior in some ways.
I posted this before and it seems like it may have been overlooked, so I'll repeat it. The rabbit links don't have twice as many calories per their nutritional chart, but they do have about 5% more protein and once the casing is digested, would presumably break down and be assimilated much more completely since it's just ground meat with more surface area. Mice with incisions in the skin lead to faster growth rates in corns since they digest more easily/completely. For that reason, I wouldn't be surprised if the snakes eating links grow faster even if calories, protein, and all other relevant factors are the same between the groups.
Or more simply put, if you got a bag of 100 mice and pulled 50 of them out to grind into sausage links, I feel confident that the sausage links would lead to faster growth and superior nutrient retention since they would be more digestible and require less metabolic energy to break down when compared with the unaltered mice. Sure it's not the most naturalistic thing, but neither is thawing out a frozen rodent to feed to a snake on aspen bedding in a plastic box. If the desired outcome is superior growth/nutrition, it seems to me that the links would have to be a viable option if they are truly comprised of ground whole prey items. The sausage casings may be a confounding variable, but since they're supposed to be made entirely of beef protein and gelatin, that should just add to their nutritional profile.