I've never heard of anyone associating this name with Adolf Hitler (unlike the name Aatu, at times). I think it's too linked with the Finnish word and it reminds me of dates like 'jouluaatto' (Christmas Eve) or 'vapun Aatto' (eve of May Day). Aatto sounds old fashioned like many Finnish word names do, though not in an unpleasant way in my opinion. The 'eve' connection and Aatto's sound also seem nice to me and I wouldn't be surprised if this name would become more popular in Finland.
Aatto S. is a Finnish translator. Amongst works translated by this person from English into Finnish are Haapakoskelaiset by Jacob Ahrenberg and Setä Tuomon tupa (otherwise known as Uncle Tom's Cabin) by Harriet Beecher Stowe.
Aatto Pietikäinen was a Finnish ski jumper who competed in the 1940's. He finished eighth in the individual large hill event at the 1948 Winter Olympics in St. Moritz.