This is definitely legal per the rules of the league. However, some new unskilled people might consider it cheap. Last year, I was in a fantasy baseball league (for the first time in 6 years) with some new/unexperienced guys and they weren't a fan of me streaming SP. At the same time, the rules are fair for everyone and anyone can stream. Streaming can be avoided if a league has more teams, more players on each team, or a cap on number of acquisitions in a week or innings pitched limits.
8 team leagues are STREAM CITY! Keep streaming away - especially with SP to win K's and Wins and Save/Holds. Streaming with batters is more risky due to the 0-5 possibility with just a good hitter instead of your normal great hitters. At the same time, it gives you extra chance for more runs, RBIs, HRs, and SBs. So it's worth it as long as the hitter is good and playing in a good matchup vs a bad pitcher.