I would recommend keeping corals that like similar conditions in the same tank. Polyp size is a continuum rather than two distictive groups. Of the two groups, LPS and SPS, that hobbyist have assigned (and these are strictly hobbyist terms), there are representatives of each group in every reef zone. Therefore, you cannot simply say all "LPS" will do well in low flow, low light, and all "sps" in high flow, high light. Making these assumptions will kill lots of corals, versus actually researching the individual coral's needs. Short answer... Yes you can keep LPS and SPS corals in the same aquarium, and many LPS would do better with certain SPS than they would do with other LPS and vice versa.