Viper, I don't quite know what you're asking. . .
Yes, as pilots we fly in both the United Express and Delta Connection systems. Many times on the same trip. We'll take a UEX airplane into a city, spend the night, then take a DC airplane out. We have about a dozen cities that we serve with both United and Delta (into different hubs, of course). Example, I was on a trip and we flew Delta Connection from DFW to BNA, then the next morning flew UEX to Denver.
Is that what you were asking?