Short answer: yes, however there are a number of caveats.
Long Answer: It depends. You would have to characterize both MOs individually so they give a specific phenotype, perform all proper controls, and then you can co-inject those MOs. Look at the primer published by Didier Stainier and colleagues (Article Guidelines for morpholino use in zebrafish
). We have stopped using MOs since 2012 and make CRISPR mutants. It may take a bit more time but it much more reliable way to assess LOF.