It is up to you. Personally, I hold off on probiotics until after I have completed the cleanse because some may get carried out with the fiber shakes...especially true when taking P&B. Some HH formulas contain inulin which helps support the growth of your own good bacteria and would not be a problem in this regard. The only probiotics that will actually implant are human-strain...PD is a transient probiotic and your yogurt may contain other strains that will not implant. Since they will pass through anyway...just make sure that if you take them along with the HH cleanse you don't take them too close to the bulking agent. Many people find that PD helps keep them regular... which is an asset when doing any kind of colon cleansing...but they will work best if you stagger the doses with the fiber shakes. If using a human-strain probiotic, hold off until completing the cleanse ...probiotics will not implant in a toxic colon.
Robert Gray...developer of the Holistic Horizon cleanse...also recommends rejuvelac to replace good bacteria. He has a recipe for it in his book The Colon Health Handbook. You might want to get a copy of the book and give it a try. I've never used it, but know others who have with good success. HH also makes a product designed to feed the beneficial bacteria. Sorry, but I can't remember what it is called...something Food. You can find it on their website.