Actually the scale is not terribly consistent. Some of them are 30mm, others are more like 25mm. You should be fine with 28mm.
And if you aren't dealing with human beings, I'm not sure how consistent the scales need to be. How tall is an orc or elf, really?
Most, if not all of the figures in the DND Adventure series previously appeared as miniatures in the DnD RPG and miniatures games, so they are by definition compatible with those lines. I think the Pathfinder lines are the same. I think all the plastic miniatures work together. Some lines of pewter miniatures were more variable and may not look right when mixed.