2D Animation with Grease Pencil is a relatively recent WIP.
The tool was used to make annotation and draw some lines.
Drawing experience was improved by adding brushes and sculpt mode in 2.77. In 2.78, layers and fills were improved with addition of color palettes and bones parenting. Support of interpolation between drawn frames was only supported in 2.79.
And the progress will continue in future 2.8. Grease Pencil will become a 3D object with modifiers and UI is completely redesigned by this change.
Currently, a grease pencil block is a data of a window.
What is the general workflow like between either program, how different (or similar) are they?
So, basically, in 2.79, the workflow is specific to Blender related to the fact that a tool not thought for that task grew up.
In 2.8, UI and workflow should be more fluent and designed with 2D animation using a 3D space in mind. But it is the future and currently, the greasepencil-object should be regarded as an experimental work-in-progress.
Is grease pencil vector or raster based (or both)?
Blender will render raster images of your Grease Pencil animation.
But inside blender, Grease Pencil strokes are made of points and segments like meshes without faces or curves without interpolated segments and control points handles. So, actually, editing of Grease Pencil strokes is a weird thing in-between editing a mesh and editing a curve ; but the ability to sculpt strokes is a great sensation that allows to overtake lacks that you can feel in edit mode. You can convert Grease Pencil Strokes to Meshes or Curves. But the reverse operation is only possible through addons and it is not supported, yet in 2.8 version.
Does Blender offer the same types of animation styles (cut-out, cel, etc…)?
Yes. But it will require using other tools than Grease Pencil, you will use same bones armature for 2D or 3D animation.
Lines can be Grease Pencil, an UVtexture on a Mesh plane or Curves. These things can be distorted by many ways or just rotated around a pivot by a bone.
Blender have several render engines supporting toon shaders and one NPR renderer called Freestyle to render 3D objects as stylized lines.
Through compositing node editor, you can give any style you like to your render.
To resume, as a 3D animation software suite, Blender has already a lot of tools. But the workflow to facilitate their use for a 2D style purpose is still in construction ; although 2D animations can be delivered with 2.79.