I am unfamiliar with Leadbeaters. However, if you can find the website that is the origin of this particular diet, there should be information regarding what can/should be fed or not.
Some diets restrict specific things and require specific things, it's best to know where your specific diet stands on pellets. Pellets are not mostly used as a staple, nor are they a necessity. In general, there are many who offer pellets, quality brand (Pet Pro-Happy Glider being used by many including myself) on the side. Most will leave a few in a dish during the day, refresh each morning. I for the most part use some throughout their forage toys, currently I'm using a "Snacky Mouse", but also often have other forage toys around the cage and place some pellets around between those. Although, there have been times I just left some in a small dish now and then. Then there are those who do not like to offer pellets of any kind to their gliders.