My understanding is that it is not currently frowned upon or if it is I have not been made aware of it.
Really? Do we work for the same company?? Have you seen the failure rate of Freighter FOs that que up for freighter command having not come from the passenger fleet???
...Take the hint my man, I think it is pretty safe to say that it counts as a "frown".
And if you think the two aren't related then you need to open your eyes and smell the statistics.