Using St. John's Wort normally (taken orally) should have a negative effect on lucid dreams since it would increase your seratonin levels. However when you burn a plant, the chemicals can be altered, lost, or changed. So the short answer to your question is "I don't know." I haven't smoked St. John's Wort.
BTW there are hundreds of varieties of St. John's Wort, and they are native to Florida, USA. If you educate yourself about the plant, and if you are in USDA Zone 8 or Zone 9 you will probably be able to find some lurking in the woods.