Нет, вы можете указать только один фильтр.
You can add the result of each search to a HashSet to get a unique list of files matching both searches. A List would not work in edge cases where two different wildcard search patterns can match the same file.
ОБНОВИТЬ
HashSet is only available in .NET 3.5 and later. Since you are using 2.0, you could use a List, but you should check if each item already exists before adding it.