Hmm, I've never heard the nihilist interpretation of Row, Row, Row Your Boat before.
The lyrics have often been used as a metaphor for life's difficult choices, and many see the boat as referring to one's self or a group with which one identifies. Rowing is a skillful, if tedious, practice that takes perfection but also directs the vessel. When sung as a group, the act of rowing becomes a unifier, as oars must be in sync in a rowboat. The idea that man travels along a certain stream, suggests boundaries in the path of choices and in free will. The third line recommends that challenges should be greeted in stride while open to joy with a smile. The final line, life is but a dream, is perhaps the most meaningful. With a religious point of view, life and the physical plane may be regarded as having equivalent value as that of a dream, such that troubles are seen in the context of a lesser reality once one has awakened. Conversely, the line can just as equally convey nihilist sentiments on the meaninglessness of man's actions. The line is also commonly sung as "life is like a dream" rather than "life is but a dream", possibly to sound happier, less meaningful, and more appropriate for its audience of young children.