Hi Bill,
I have read on here that it is not a good idea to use mulch for media because of chemicals - but if you are sure it is untreated - you could give it a go. Orchids can grow in just about any media if the watering and feeding conditions are correct. For our phalaenopsis, we have developed a mix we use that includes large and medium coconut husk as well as several other items. See the details on the RVO Care Page -http://www.rv-orchidworks.com/orchids/nursery/orchid-videos/how-to-repot-a-phalaenopsis-orchid/ and here is a step by step video that goes with the text on the page I link to above.
Cheers,
BD