These displays can seize up if it is super cold. Before I had a house with a garage I saw it happen once or twice on super cold days. I saw someone post that there was a TSB out for it and that maybe a deal would fix it I guess, but I don't know what they could really do unless there is a new designed face for it. If it continues to not work permanently then definitely take it in, but once it warms up shouldn't be a problem.
Yeah, the LS needs Dexos approved oil, if they just swapped it out I wouldn't worry about it. Its not going to kill your engine, especially that short of a time and no one will ever know anyway haha. Just FYI, there is a website of specific brands:
http://www.gmdexos.com/licensedbrands.html