Yes, but if you wish to submit designs for sale on the ready-made design marketplace that you’ve already created as part of an unsuccessful project (be that a design contest or some other project), there are four things you need to ensure:

1. The logo must use a generic company name.
2. The design is yours to sell.
3. The design must not be listed for sale anywhere else.
4. The design must be be unique (i.e. significantly different from all other designs)

You cannot simply submit a losing design from a design contest “as is” to the ready-made design marketplace. At the very least you need to change the company name to something generic, and make sure it’s significantly different to all other designs (including the design which won the contest).