I have no real experience in either paddleboats or rowboats, but I believe the relative benefits of undead in the sailing/shipping industry are obvious.
No Pay Required-Undead workers follow orders without question and without pay.
No Food or Water Required-For obvious reasons, undead do not require food or water, or even air for that matter.
Reliability-Zombies and skeletons operate (or can operate) at maximum performance 24/7. They need no breaks, they do not hesitate, and they can keep working as hard as they can for as long as required. If they can be "programmed" to follow simple commands (even lists of simple commands) then you essentially have robots that can spring into action and rectify the situation when emergencies arise.
However, in most settings, the undead do not have the awareness and/or intelligence to recognize problems (or potential problems) in their environment and act accordingly, so this is probably a moot point.
Decomposition-Unless some magical and/or natural preservation techniques are maintaining your undead, they'll come apart when exposed to moisture, microbes, rats, or fungi. For the sake of #3 above, your zombies should really have some Enchantments of Preservation or high-grade mummification or resin coatings to keep them "fresh."
Lack of awareness/intelligence-As stated in #3 above, most undead lack all but the most rudimentary intelligence and awareness of their environment. This leads to problems akin to what I sometimes experience with computers; since they only understand one language, and they have no creativity, lots of orders will get misinterpreted or lost in translation.
Basically, undead need either advanced "programming," higher intelligence, or a living being directing them in order to be helpful when situations change and initiative is required. However, in emergency situations, hesitation, panic, and even fainting are common, and that essentially takes out any advantage to a living director.
In any emergency situation, you have at least a 10% chance of the director (captain?) being overcome and becoming absolutely useless, which results in failure and likely death as well.
- Lack of precision-Undead are not known for fine motor control. Clumsy, robotic undead are a common fixture of any setting that include undead, and that would make rowing the obviously inferior choice. However, if undead retain the skills they had in life, or if they are capable of learning and executing tasks with precision, rowing is a more aesthetically pleasing (and perhaps more advantageous!) option.
In summary, it depends on the undead in your setting.