I think you'll have to pay close attention the the velocity of the very next note just after your crescendo. A crescendo will often end louder that the musical passage that directly follows it. Examlpe; if you are going to use an existing section of midi notes to create the crescendo, (or you can "control / shift / mouse click" in a row of cymbal notes at your default velocity setting).
Set the duration to, say, 32nd notes.
Set the channel to 10 (assuming your working on drums) or the channel your instrument is on.
Set the View/Edit to Velocity.
Hold Control and Shift down and mouse click it a row of cymbal notes (C#4 on the Keyboard Pitch Panel to the left) as close together as you can get 'em. Do this on a blank bar/measure for practice. You can copy/paste/merge/replace later.
Play it to here it. No crescendo.
Now go to the bottom Graphic Event Panel and draw a diagonal line from low left to high right with you mouse button held down.
Voila' a crescendo (that needs some personal practice and tweeking to fix it right?) That's what Edit / Undo is for.
Now fix the hanging notes after the crescendo ( if you have some) and go back and tweek your crescendo by raising and lowering velocities and moving the notes a little left and a little right. Most cymbal roll crescendos ar so fast that a sloppy mouse click entery is good enough for sounding somewhat natural.

A trick I learned is to make the velocity draw in a "Z" shape.
Say I've got 32 cymbal hits in a bar. A long crescendo.
Starting from the left I'll draw from a low 10 velocity to half way across the bar up to about a 75 and let go of the mouse. Then I'll start again at half way through the bar and draw from a 30 on up to a 127 to the end of the bar.

Now the notes that follow the crescendo "might" maintain the velocity of the last crescendo note. So, zoom in really big and close to make it easier to tweek and bring the velocity of the very next note to approximately where it was before or refer to the velocities of notes prior to the crescendo.

Here's a copy paste from part of the HELP section;
"Graphic Event Panel
Graphically display and edit non-note MIDI events. This panel only shows MIDI events specified in the Chan, View/Edit, and Controller Type controls.
Except for Velocity data, the view is drawn staircased. Blue lines extend between events. This makes it easy to see the persistent effect of events, if they occur to the left of your current viewing location.
Zero-value events are drawn as small hollow squares, to make them easy to identify.
With events such as Pitch Bend, or controllers like Modulation and Sustain, it is important to take care to end a "gesture" with a zero-value event. Otherwise, subsequent notes will be affected, with an unwanted "hanging" permanent Pitch Bend, permanent Vibrato, or Sustain Pedal locked down. If you notice this, just move the mouse cursor where the gesture should have ended, and click-in a single zero-value event.

This is fun Huh!

Does the noise in your head bother me ?