Probably not. A good defense attorney isn't going to advise anything about pleas until he or she has all the evidence. While there will be some given to him or her at the preliminary hearing, it usually takes prosecutors a few weeks to get the majority of discovery together. That said, an offer may be made by the prosecution, and there may be some negotiating between the two parties, but it is unlikely an official plea on the record will be done.
Preliminary hearings are mainly for brief communications between the attorneys and the court in setting a schedule, setting up conveyance of discovery, etc. etc. It's a routine procedure that doesn't have much impact on the case as early as this. In some cases, it can be used to put witnesses on the stand, as described in the link below, but there are tactical considerations with that route. You can "pre-try" the case as a defense attorney, and maybe get some charges thrown out, but the downside is that you've given the prosecution time to adjust their strategy in response to your questions.
If you get lucky, you can keep some charges out. In the alternative, with a case this inflammatory, the grand jury could indict a lot more charges than the prosecutor, who will tailor the charges to the state's best evidence.
Frankly, while there likely won't be a plea at the preliminary hearing, I would bet good money that negotiations will start if there is solid DNA evidence. :twocents:
Not a verified insider, so take what I'm saying with a grain of salt, but when I did criminal defense work, the vast majority of the preliminary hearings I attended were fifteen minutes, and almost entirely about scheduling and passing discovery between sides. Very few cases actually get down to the nitty-gritty of putting witnesses on (again, see below for verification of what I'm saying since I'm not verified at WS).
http://criminal.findlaw.com/criminal-procedure/preliminary-hearing.html