Why might it be problematic to use a cell undergoing meiosis to create a karyotype?
Yes, you can, but it's way more difficult.
First of all, in order to see meiotic chromosomes, you need to colect young floral bud in the right stage of development (not too young, since you don't want microspore mother cell, and not too old, since you don't want polen), and that's not that easy. Then, once you found the right stage and made a slide, you need good knowledge on all the phases of meiosis to understand what you are looking at. Bivalents and translocation rings can make it very difficult to really understand the chromosomes set you have in the cell, so you need a good sized sample and a lot of observation and analysis. If the species you are analyzing has small chromosomes, it's even more difficult to understand what you are looking at.