Perhaps in casual conversion, Thomas. But if you are writing, I would follow the convention that you work on a shift, but in a group. In the example I gave, night-shift becomes an adjective describing the type of group. But frankly, even in a night-shift group sounds a little strange to me, and I'm having a hard time imagining when/why it would be more informative to say that than simply "I work on the night shift." Also, colloquially, people often leave out the "on" and say "I work the night shift."