When we went to look at Boo, we took Annie along with us. It was important to me that Boo wouldn't be aggressive towards Annie. They basically ignored each other after the initial sniff. I was fine with that.
Boo was way more interested in DH then Annie and they got along from day one.
Also, if at all possible try to have them meet somewhere other then the current dogs home so that they don't feel like they need to protect their turf.