The traditional downside of woodchips(especially fresh ones) is that the increased surface area allows them to decompose faster, and this causes them to rob the surrounding area of nitrogen for a while.
The key would be to use lots of manure/nitrogen sources to counter this; if you're doing this in a hugel, that infill space that the woodchips will be taking should otherwise have been full of these things anyhow.
As best I recall, while Alder is a nitrogen fixer, most of that would be in the roots and leave rather than the woody part, but I could be mistaken.
A hugel of woodchips also wouldn't last nearly as long, as the woodchips, especially fast-rotting alder, will decompose much faster than logs... but it sounds like this would be in addition to larger wood?
'Theoretically this level of creeping Orwellian dynamics should ramp up our awareness, but what happens instead is that each alert becomes less and less effective because we're incredibly stupid.' - Jerry Holkins