i've not tried it out yet, but there was a thread in the mailing list on the same topic a few days ago and, if i recall correctly, the suggestion was:
- to use any way that outputs your code formatted as html (an online service that worked for me is http://hilite.me/
- copy paste / open the formatted code into libre office writer and save the snippet as an odt file
- load the odt file in a scribus text frame.
i've now tried it out and it worked on a short snippet with scribus 1.5.2.
you can also try to directly load the html file into scribus (i have not tried it).
sadly, for now, you have to do the whole workflow for each frame for each modification of the code that changes the highlighting.
(and, of course, putting the code in a latex render frame will also work!)