One of the leaders in the classical brass world is French artist, David Guerrier, who I heard perform at the ITG Conference held in Manchester UK in 2002. He had already one major competitions as a trumpet player and over the past years moved to playing principal french horn with a leading French orchestra - well there are far more solos to play. Now David Guerrier is trail blazing with his virtuoso performances on historic brass instruments such as the opheicleide. The result is that many more young brass players are emulating him and attitudes have changed considerably.
Ofcourse military, brass band and jazz musicians have always moved around onto different brass / woodwind / string / percussion instruments as required to do the job. Maynard Ferguson and James Morrison come to mind for me as great examples.
I was encouraged to try through reading an article in the ITG Journal titled, "Slide Your Way to Success.' My experience is that playing some trombone has not harmed my trumpet playing at all and the contrast in terms of mouthpiece and using a slide is quite refreshing in a way. I don't have any issue at all in switching from one to the other.