It's common to use SQLAlchemy with Flask, so the answer depends on how comfortable you are with that ORM.

That being said, you should absolutely at least learn the basics of working directly with databases. ORMs are a leaky abstraction, and you will run into situations where it's easier to drop into raw SQL to get the job done. Think of it like this: using GPS while driving is fine 95% of the time, but when it malfunctions or breaks, you're screwed unless you know how to read a map or ask for directions ;)