No. This is not a fact. After all, what would you use otherwise?
However, I would advise against using pampers. If you are going to use a commercial brand, Huggies has odor free diapers which will not cause as many rashes. They are also just as absorbent but less thick.
When babies are growing they will gain muscle tone and develop strength which will counter act the "gap between the legs". As they start crawling and walking, this usually corrects itself.
If you are still concerned another thing you can do is make sure the diaper is not fastened to tightly. It should be snug but not tight, you will then notice that baby will move with greater ease.
You can also take baby to a trusted chiropractor who is experienced in adjusting babies. Do this periodically, and this too will help, and he/she will also be able to advise you concerning this issue.