Strings, brass, and woodwinds all use portamento to some degree or other. There are a few instruments that also use pitchbend for 'note-on' pitch bending. All solo stringed instruments use this effect as well as the trombone. There are some advanced portamento rules that went into effect with the newest update. Check the update documentation for information on this.
No, there's another controller for portamento (can't remember right now.) Pitch bend is used in conjunction with portamento for solo strings, trombone for added realism. Pitch bend is seperate though and could be applied to any instrument in GPO. Make sure and take a look at the update documentation for information about using pitch bend and portamento for the solo strings and trombone.
Basically, use the portamento controller for slides between legato notes (sustain legato active.) Pitch bend is applied at note starts during detached phrases or regular note ons at the beginning of a passage.