Again, you have this backwards. Ext3 was chosen in part because it was a community-supported file system. From the very beginning, ext2 and ext3 had support from a broad set of developers, at a large number of ***different*** companies. Of the original three major developers of ext2/ext3 (Remy Card, Stephen Tweedie, and myself), only Stephen worked at Red Hat. Remy was a professor at a university in France, and I was working at MIT as the technical lead for Kerberos. And there were many other people submitting contributions to ext3 and choosing to use ext3 in embedded products (including Andrew Morton, when he worked at Digeo between 2001 and 2003).
ext3 was first supported by RHEL as of RHEL 2 which was released May 2003 --- and as you can see from the dates above, we had developers working at a wide range of companies, thus making it a communuty-supported distribution, long before Red Hat supported ext3 in their RHEL product. In contrast, most of the reiserfs developers worked at Namesys (with a one or two exceptions, most notably Chris Mason when he was at SuSE), and most of the XFS developers worked at SGI.