If you’re generating characters with a character generator, it’s not an asset created by you, it’s not original.
You don’t have to use expensive tools to create your assets, things like Blender are free. The time taken to learn tools, well that’s just a skill gap. If you don’t have the means to make your own characters, accept that your assets are not original (and of course credit them as such in your entry), or build a game that does not require characters 
- it’s a game jam, play to the skills you have, not the skills you don’t