Vegetable tanned suede leathers are acceptable for use as holster lining material.
For some reason, people sometimes think of ‘suede’ and ‘leather’ as different things. ‘Suede’ is simply leather with the top layers removed – and often the new surface is buffed.
The issue for holster linings is the tanning of the leather. Chrome tanned leather contains chemicals (chromium salts) that can react with a blued finish on a gun. With composite materials and newer surface finishes, this is less of an issue than in the past.
Your holster is made with vegetable tanned leather and thus the inside IS vegetable tanned sueded leather without adding anything. Veg-tan suede may be useful, for examples, if the user would like the holster made a bit thicker or for color contrast.