Well? Do they?

It would be very difficult to do particles in the spirit of the jam, so generally they’re best avoided.

If you insist on doing particles, yes, they’re a visual element so they must be text.

I played the last jam's winning game, Hero of memory and the character had jumping and landing particle effects

It is possible to do particles using periods and commas for the sprites, you just have to figure out how to get them in there correctly.