Probiotics do not cleanse, they simply introduce additional beneficial bacteria (much of which does not make it past the digestive system unless you use the encapsulated ones).  They may "appear" to have a cleansing effect if there is die-off of bad bacteria being crowded out by the beneficial ones, but I rather doubt that will happen.

 If I want to do a colon cleansing, can I just go with a good probiotic to colon cleanse instead of doing the harsh psyllium drinks? Do good probiotics clean the gut of impacted waste?

The answer is yes and no. Probiotics do help to maintain regular bowel movements, which helps to keep the intestines clean. And they help to detoxify various toxins such as hormone metabolites. But the "fossilized" mucoid plaque thing is a myth. The only time you are going to see something like this is with an overdose of iron salts.

In general to keep the intestines clean make sure you are getting plenty of fiber in your diet. I don't like psyllium at all, but there are excellent sources of fiber including fruits, vegetables, and brans like rice bran and oat bran. These fibers will also feed the flora. You also need to make sure you are getting plenty of water throughout the day. Spring water is the best. If you need a mild laxative I recommend the herbal formula triphala, which also cleanses the liver and boosts the immune system.