While you can draw inspiration from other sources, direct crossovers - whether in-universe or not - are unfortunately not approvable by the MMCC. Generally the rule of thumb is at least 80% of the kit must be Mandalorian, while the remaining 20% may be non-Mandalorian depending on the source.
Without seeing a concept, I can't really give you further guidance either way. Keep in mind also that I am neither App Team nor a Ruus'alor, so definitely take their advice over mine.
Either way, I look forward to seeing your concept!