Yes and no.
I have no idea why the Mets didn't draft Giolito, but if they have a strong conviction about Cecchini's skills, I'll assume that's why they drafted him.
When dealing with HS players, you just can't look at the strength of your major league roster. You just draft the best available player. If the Mets are still broke, they can trade Tejada if Cecchini can play or if they have Tejada locked up long-tern, they can move Cecchini. Shortstops are good athletes and an early position change should be pretty easy (2B, CF, LF, 3B if he gets big). Flores played short for years and was moved to 3B this year and has gotten some opportunities at 2B and 1B.