hello there, nice, solid team!
There are a couple of problems I see here. Your defensive core isn't supporting your team enough. Vap / Gliscor are not only dragging your team behind momentumwise but aren't covering enough threats for the rest of your team to be able to focus fully on offense. Opponents with BoltBeam coverage and / or strong unresisted STABs can muscle past your sponges into your 'overflow' pokemon- Latios. This results in the forced use of your Latios to tank many hits for you- and because it's a scarfer, it won't last long and you'll need to fix it. Your sponges are also holding you back momentum wise. It's really tough to set up with Lucario or Gengar after you use your Vaporeon to wall something. Your team is really split between pure offense from Luc / Gar and pure defense from Vap. This, imo, needs to change. Your team needs something more offensive over Vap- something that you can use to take water type attacks but doesn't completely ditch momentum while doing so. A good replacement to your water type sponge is Scarfed Keldeo-R over Vaporeon.
Keldeo @ Choice Scarf
Timid / 4 HP / 252 SpA / 252 Spe
Hydro Pump / Secret Sword / Hidden Power Ice / Surf
Keldeo is a nice replacement to Vaporeon because it handles Rain teams more efficiently and doesn't sacrifice momentum in order to do so. It can tank one or two hydro pumps or scalds in Rain, and reply back with powerful, fast Hydro Pumps or Secret Swords. It's so important because with it Rain becomes much less of a problem, and you don't have to rely on Latios to sponge hits all of the time when you want to keep momentum. Keldeo's fast speed also lets you revenge kill many threats Lucario or Scizor can't check reliably- Volcarona and Landorus-I, for example. Its STABs will help against Sand and Sun too, and give you another great answer to Tyranitar / Ninetales and friends. Hydro Pump is your main STAB, and hits everything that doesn't resist it for a lot of damage. Secret Sword is secondary STAB; it hits Blissey quite hard and can be used to break walls. Hidden Power Ice lets you revenge DDancers such as Mence / Dnite, and hits Celebi / Loom / Lati@s. Surf is for when you need to hit and don't want to risk a miss.
With the addition of Keldeo, Latios's role as a scarfer becomes less meaningful. For this reason, I suggest you change Latios into LO Roost.
This means LO > Scarf, Roost > Trick, and Hidden Power Fire > Surf. Being that even with the Keldeo change you'll still need Latios to sponge some special hits, giving it the ability to heal itself up and hit even harder will help a lot. HP Fire over Surf as Keldeo already has great water type coverage and HP fIre lets you beat Sun and Steels.
Finally, I don't really see the point of Gengar on your team. Its speed isn't really needed since you have 2 priority users and a scarfer, and its typing and attacks are covered more or less offensively by Latios and defensively by Gliscor. Your team doesn't really have any problems handling Breloom, since you have Gliscor, and Lati@s can be beaten by Scizor. In fact, Gengar makes your team less effective against opposing weather teams, as it is weak to Tyranitar and can't sponge any attacks from Sun / Rain teams. Instead of Gengar, I would use Dragonite.
Dragonite @ Lum Berry
Adamant / 4 HP / 252 Atk / 252 Spe
Dragon Dance / Outrage / Earthquake / Fire Punch
Dragonite is a fine addition because of its great bulk and resistances as well as offensive power and capabilities. Dragonite's presence on your team pretty much erases Rain / Sun as threats to your team, since Dragonite can wall many common attackers from those two kinds of teams. Dragonite also has the ability to increase its speed and power for a sweep- giving you a nice cleaner that can finish off or start off matches with a bang. Multiscale is an awesome ability and a main reason why I think Dnite would work so well for you. It gives Dnite plenty of opportunities to come in and set up, giving you a fair share of bulk and offense. Dragon Dance is there for obvious reasons; it lets you voost offensice stats to scary levels and then finish off opponents. Outrage is your STAB move; it hits everything hard even unboosted. Earthquake and Fire Punch are for coverage, as EQ beats Jirachi, Tyranitar, and Ninetales, as well as Steel types like Heatran. Fire Punch can be used to combat sun teams and beat Ferro / Forretress / Skarmory. ESpeed can be used instead of Fire Punch, but you already have a scarfer and two other forms of priority so I don't see the point of adding more. Hitting steels is better imo. Lum Berry is so that you can shrug off Jirachi's paralysis or Venasaur's sleep powder. It helps against burns too. Its weakness to SR is mitigated by Gliscor's fast taunt that prevents hazards.
Now, for one last tiny change. I'd use Crunch over Bullet Punch
on Lucario; BP is redundant since you have Scizor, who handles Terrakion well. Crunch on the other hand hits Jellicent, whom you could have troubles with, and Reuniclus, whose TR could dismantle the offensive nature of your team.