Wooden dogsleds are mostly made out of ash, birch, hickory, or maple, and I've carried some serious loads in them back in the day (as well as put them through some serious abuse).
I don't see why a wood rack wouldn't work. One thing you might think about though.
Wooden dogsleds (the good ones) are lashed together with tuna leader (like they use for tuna fishing). If you bolt one together, the wood tends to split at the bolts. The lashings seem to spread the force about, and let the wood flex a little without breaking.
Just food for thought. I don't imagine you want want to go back and lash your nice rack together.