Even if Seoul is serious about this, considering the locations of the two countries, it seems incredibly difficult and inefficient to ship weapons from South Korea to Ukraine.
Considering that Russia and North Korea are increasing ties, announced at Putin's recent visit, it's likely in SK interest to aid Ukraine so that Russia has to allocate mil hardware to their fight rather than selling it to NK. This just happened with India, who decided to go with US hardware because Russia has continuously delated delivery of systems they already bought.
Have you any idea how cheap shipping is?