can the brand of brass used make a noticeable enough difference in accuracy?
No. But, it would still be best to use one kind of brass for each particular load. Specifically, for 308/7.62 there is a significant difference in weight and volume between brands. But if you have all of one brand, that variance is essentially eliminated. Conversely, you would not want to mix brass, because brand variances will cause different results and pressures.