Generally speaking, artist registries are a good thing. Since I am not familiar with the two you specifically referenced it is hard to comment. On the Texas one, check to see when the site was created. It might be that they just started, or it might be that not many Texas artists have listed with them yet.
The greatest benefit online for any site is the fact that you get listed and another link to your own site is added.
The greatest benefit to being listed with a "good" standard registry (one that is not online) is the visibility you gain by being in their archives. Most standard registries require your 35mm slides, bio, etc. be sent to them. Your data is posted in an accessible notebook of some kind that local designers, musuems, corporate art reps, etc. can physically see, and seek local artists to collect or purchase their work.
"Physical" registries usually charge a nominal fee which is well worth it particularly if the registry is specific. In other words, if it is a "portrait" only, "landscape" only, "Texas" artist only registry, etc.
If you are considering postin with an "online only" registrie please post the URL and I'll take a look at it (them). I'll be away till Monday, so also email me with the info so am sure to see it.
L. Diane Johnson
2001/2002 Plein Air Workshops