Ok...so no Normals/Baseliners/Mortals imo
Lore reason 1 - Dropsuits: The Dropsuits we use now have largely been designed with our Combat Clone's Anatomy in mind...that being that our combat clones aren't designed to last all that long in the first place (They would still be able to use some of the First-Generation Stuff...and maybe some of the MLT Derpsuits...but largely:
Quote:Radiation of shields and the portable reactors which would normally burn most regular humans and cancer ridden them for the remainder of lives was of no concern to the immortal soldiers.
So...without the benefit of our Reactors, Servos, Shield Generators, Etc...Normals (or Baseliners) would have a tough enough time on the Immortal's Battlefield.
Lore Reason 2 - Weapons: The weapons used by us immortal weapons is either purpose built for us, re-purposed starship/MTAC Equipment (For mining and/or Point Defense), or Scaled Up/"Overclocked"/Overcharged versions of what the Regular Soldiers Use. While there are Comercially available Plasma Rifles and Ion Pistols, the ones we use would cause unprotected human skin to burst into flames by just the heat emitted by the weapon, let alone what the impact of the charge would do. MLT Gear would be at the utmost High-End of what a Normal could use, if they where suicidal, or had access to extremely expensive military hardware (Spec Ops Suits that where the predecessors to our Dropsuits, or MTACs).
Lore Reason 3 - Technology and the Implications of Skill Points: Minimum SP Investment to use higher tiers of equipment may be just a convenient way to encourage progression throughout the games, but as others have mentioned earlier it implies that there is a huge amount of active management of our Suit and Weapon Systems. Weather through managing containment fields on the Plasma Centrifuges, or ensuring our suit's reactor doesn't go critical...there are implied to be several reasons why a certain amount of knowledge in a given subject is necessary.
Lore Reason 4 - Combat Clones: While the advantages of being immortal should be immediately apparent, the use of Combat Clones gives us a number of distinct advantages over normal. First off, the clones we use in battles are designed as generic, cybernetically enhanced, nearly 40k Space Marine sized super soldiers (Very Close in Size to the SPARTAN IIs)...designed to shrug off little things like fractured bones or arterial bleeding and continue fighting until the clone's nanites can no longer sustain them, or it suffers enough trauma to actually just give out...or the owner just isn't feeling this battle anymore xD. Even if the Dropsuits defenses fell, most of the combat clones would remain largely unaffected by any but the largest, most powerful munitions that Normals could bring to the battle.
Those are the big 4 lore reasons I could think of why you wouldn't have Normals running around our battlefield, suited or not...they just don't operate on the same scale as us Empyreans...
Drones (Rogue or Otherwise, Smart or Otherwise) would be a welcome addition if the scale of the battles could be increased...but I think I would rather just have more players in battles.