We've had another customer report issues with the SMS app, actually, but we're having difficulty believing that the SMS database corruption could be caused by PlecoDict - unless there's something severely wrong with the design of the SMS program, the database should stay intact even if the software crashes.
So these out-of-memory messages happen within the other applications, correct? And they list those applications' names, not PlecoDict? Is pTunes playing in the background during any of this? Did these errors ever happen without PlecoDict installed? What about if you soft reset your Treo but didn't run PlecoDict right away, would you ever see an error before running PlecoDict?
pTunes and CJKOS can stay resident in memory even when they're not running (unlike PlecoDict, which only loads at all when you start it or bring up pop-up mode) so it's possible that there might be an issue with one of those. With CJKOS, if you're using it within PlecoDict (via Input Field Compatibility mode) it's possible that that might somehow destabilize CJKOS or cause its memory usage to increase. Have you noticed any bugs or crashes relating to either of those programs?
Also, is your Treo running the latest ROM version?