I have an instructor who likes to do this (mix 2 songs)... I'm not a fan because I feel it interrupts the flow of the dance, esp. when you only have 2 minutes to perform anyway. He mixed together a merengue and a samba and tried to get me to do that for Showcase. I said no and we stuck with the samba I had picked out. The judge awarded us a rhythm "best in show" for the routine.
fwiw, in showcases i have tended to mix styles within the same song, and even to include passages of waltz and VW in 4/4, allowing the rhythm of dancing to cross measures in the rhythm of music. i find it interesting and musical to do so.
or rather, my instructor at the time would choreograph very capably & creatively in this manner... i was just along for the ride, and enjoyed the choreo & music very much.