Is this true about projectile motion

When working with a projectile motion, is the hypotenuse going to be the same as the velocity?

It depends which right-angled triangle you are referring to.

If the triangle's sides represent the horizontal component and the vertical component of velocity at a particular moment in time, then the magnitude of the hypotenuse represents the magnitude of instantaneous velocity at that time.

If you mean something else, then the answer is probably no.