I would like to point out that changing -ssu to dude is something that professional translators did to the prinnies of the disgaea series. Granted they were supposed to be silly, bit there is a precedent there and it probably inspired this translation.
Thing is, the Prinnies, as far as my knowledge of the series goes, are dudes themselves. Their comic relief nature goes hand in hand with the let's-give-animal-mascots-silly-sentence-enders thing and fits with the localization. Momo is very much a soft-spoken and shy character, and the most 'tude she shows off is when Yumi is hit on by other girls. Her ssu is designed to compliment her creepy-but-cuteness, like a slight lisp.