Open tunings normally give the guitar people a barre chord, i.e. they barre @ the root note over all strings - making it easy for them. They then have to change (barre) their fingering, for the rest of the chords they use, no reason for you to change what you are doing.
As mentioned many times in TB stay in standard tuning and play the patterns you know and love. I know you may still be asking; "But, what does they being in a different tuning do to the key"?
Nothing, when they changed the tuning they now must change how they fret what they play. What they did to make it easier for them has not affected THE KEY'. That is some thing that is sometime hard to get our heads around, if so, ask questions...… Kinda important we clear this up or the guitar guys will drive you crazy with all their special tunings and capo use.
Don't expect any help from a guitar guy on what key is being used, most of their answers are suspect as most rhythm guitar guys just follow the chords and strum the rhythm.