Yes, self-raising flour is perfectly fine for vegans to consume. Like most flour, it doesn’t contain any ingredients that are derived from animals or animal byproducts, so there is nothing in there that would be unsuitable for someone following a vegan diet.
Self-raising flours tend to be of the white rather than the wholemeal variety, and the only additional ingredients that you wouldn’t find in regular plain flour are baking powder and salt. This will help whatever it is you’re baking to rise better, and you can use this flour when making your favorite vegan recipe for dishes like bread, muffins, baked goods, or even pizza crusts.