I've played many mono-runs throughout Emerald and FireRed.
Mono-ground in Emerald is extremely easy, even without Swampert. Having no powerful trainers with Grass Pokemon(edit: besides Wallace's Ludicolo) is also a plus.
I stuck to the theme with using Nincada as my Cut slave, since nobody in the party could learn it(no idea why Trapinch cannot cut), but Cut isn't necessary to finish in Emerald, so I only used Nincada when I felt like accessing those blocked off sections. My team was Swampert, Sandslash, Camerupt, Flygon, Claydol, and Whiscash. You can also try Donphan or Rhydon, but those 2 can only be obtained very late.
One downside is that you have only one EQ TM, which is only obtainable right before you fight Archie in the sea cave, so a lot of team members didn't have any proper ground STAB for quite a long time. Vibrava especially was difficult to train with no STAB attacks at all. The biggest dilemma was deciding whether to use my EQ TM on Sandslash or Flygon. I ended up with Flygon, since Sandslash at least had Dig, and will have to settle for that.
Btw, Whiscash is extremely great against Wallace. Amnesia 3x against Wailord or Tentacruel, then Toxic whoever, especially Ludicolo; important that Ludicolo gets poisoned before he gets to stack DT's; use EQ on Tentacruel, and you get poisoned by Toxic, rest it off. Gyarados laughs at Whiscash though, so use other party members to deal with him before he starts to stack DD's.