If your question is regarding those specific two products (OpenSplice and OpenDDS), then the answer is yes.  There are many other providers of DDS implementations. Most notably RTI Data Didstribution Service, Twin Oaks OpenDDS, Gallium Visual Systems InterCOM DDS, etc.  You can find a list of providers here:  http://portals.omg.org/dds/category/web-links/vendors

Now if your question is wether you need to use some DDS Implementation to use DDS, then the practical answer is no. In order to have an application use DDS you need to have some library that implements the DDS API and produces/consumes the DDS-RTPS Wire Protocol messages.  This is not a trivial thing to do.  The standards are open, so of course anybody could implement them, but in doing so you would be in fact "creating your own DDS middleware implememtation".  So one way or another applications that use DDS are always doing so by leveaging some DDS middleware implementation.