Looking at the new skill definitions it looks like Heavy Projectile Weapons skill has been moved to Ground skill category which is fine but I have a question:
I have a Stouker as my primary weapon. It looks like I should invest in the new Heavy Weapons category but I was wondering if investing in Projectile Weapons helps me using this weapon or not.
Also I have a Morgukai Glaive I would like to be able to use. Is Dexterity the best skill for this weapon?
Currently nothing at all, and work on ground combat has not yet started. I wouldn't be surprised if it affected HW, though, as there is no separate skill for it, but I couldn't say so with 100% confidence as there are no rules available yet.
Ground Combat is partially implemented, but several of the skills were revised....
Stouker's are listed as a Heavy Weapon, if you intend to use it as your primary then I would recommend at least a level of 3 in Heavy Weapons (Ground Skill). At some point (if not already implemented...) this skill will relate to how much damage you actually do with that type, with a higher level you should hit for higher amounts on average before reductions (armor/force skills/etc) take place.
Dexterity is supposed to affect your chances to hit a target (opposite of Dodge) and likely will determine how many of your "Maximum Hits" will be applied for damage. Similarly to weapon skills, a low Dexterity score may mean less hits being applied (and thus less damage potential) on average than a higher score.
Glaives were previously listed as a thrown weapon, but the rules for that type of weapon have not been clearly defined and no recommendation can be made for you at this time.