It's possible to do without. However, you will make life hard for yourself -- your organization will want to use standard tools that live on top of DWs, and those tools will expect a star schema -- a lot of effort will be spent fitting a square peg in a round hole.
A lot of database-level optimizations assume that you have a star schema; you will spend a lot of time optimizing and restructuring to get the DB to do "the right thing" with your not-quite-star layout.
Make sure that the pros outweigh the cons..
(Does it sound like I've been there before?)
-D
