I`m not quite sure what you are getting here. But Sun is not a supported platform for Open Motif (due to the license). So, of course they would not have anything about Open Motif on their web site.

It sounds like you mean, "Should I use the new features of Open Motif 2.2 when some of my target platforms, such as Solaris, don`t support those new features?"

While the question is about Motif, the problem is more general -- what do you do with features that are available on only some platforms? In this case, you`d have to look at your target platforms. If you`re developing for Linux only, for example, you have more freedom than if you need to use the subset of features available with 2.1.30 or 2.1.n.