Unless a good drain-to-waste is done frequently, I presume salts will tend to accumulate whether you feed from top (salts build up at bottom) or bottom (salts build up at top). Wherever you feed, that part of the media/soil will have the highest water/fluid concentration which will tend to flow, diffuse, move by capillary action/adsorption, etc. to areas of lower water concentration, including to distant areas that will dry out faster, where salt concentrations will build up. In nothing else, there will be some salts buildup wherever media/soil is exposed to the air.
Salts buildup may not be a problem, such as if the salt deposits remain dry/drier and undisturbed, or if simply lucky. For ex., with AutoPots many (I've done it) go a whole grow without doing any top feeding or drain-to-waste. But if do top feed and disturb the top salt deposits, need to this as a serious flush, with lots of feed/water, to get rid of all the now dissolved salts.