You can even do it with a center too, really; it depends. People don't like to mix-and-match because, odds are, you're gonna end up with 2 speakers that don't mix, and it will be noticeable.
For instance, the brand B&W has a house sound. If i buy all B&W CM9s for my theater but a Philharmonic 1 as my center, you can bet I will notice.
However, if I buy a very neutral speaker such as the Phil 2, and buy a good center, from say, KEF, that has a good detailed tweeter/mid and measures very flat, I'm probably not gonna notice a difference becasue both speakers have been "voiced" to be neutral.