Unlike solarbeam, why not opt for Petal Dance on that set? Getting locked into a bad attacking type that gets 4x resisted by a lot of things isn't so bad if you get rid of all potential threats, and-
Let's talk about some "4x resists" shall we?
Dragonite
With 184 HP EVs and a neutral nature it can always live two Petal Dances after SR and KO back with Fire Blast. Offensive variants that aren't running a -Sp.Def nature can survive two Petal Dances with Stealth Rock in play, but it's not the greatest of chances. So he's our first actual threat.
Forretress
49.4% - 58.5% or
32.2% - 38.1%
To physical and special variants respectively. Shouldn't even be alive against a Sun team anyway.
Heatran
The only sure-fire counter to Venusaur, pun intended. Besides the fact it dies to HP Ground or EQ should Venusaur have that, but I digress. It's immune to Sludge Bomb and HP Fire and take
38.1% - 44.6% from Petal Dance with no defensive investment. So make the threat list a grand two Pokemon.
Nattorei
If this is still alive against a Sun team when you're going for the sweep, you may want to reconsider your team choice. Oh and lol HP Fire.
Salamence
Takes
42.3% - 49.8% from a +2 Petal Dance. That's a 2HKO with SR, and it can't even risk switching in thanks to Sludge Bomb.
Skarmory
Easily trapped and killed by both Magnezone and Shandera. Against a Sun team it should be dead regardless of trapping incredibly quickly. Can't even risk coming on Venusaur until after it's already locked into Petal Dance thanks to HP Fire. But yeah you're right, Skarm may get to switch in and...
46.7% - 54.8% against physically defensive Skarm
31.7% - 37.4% against specially defensive Skarm
And if Venusaur gets to +4, well good luck with that.
Urugamosu
We've got an actual threat here! It takes
35.7% - 41.8% from Petal Dance and can obviously KO back with Bug Buzz, but it's 2HKOed with Stealth Rock in play and OHKOed by Sludge Bomb.
Yeah, some pretty terrifying 4x resisters right there. Don't even get me started on those crazy 2x resist Pokemon; some of them can't even take any hits! They'll show that Venusaur who's boss!
Seriously what on earth are you afraid of? In "OU" the only things you need to be scared of Petal Dancing against are all either dead by that point against any half decent Sun team anyway, dead after two Petal Dances regardless, or dead after two Petal Dances with entry hazards in play. The only things you should be scared of are Urugamosu, Heatran, Dragonite, weather inducers and opposing Chlorophyll users. The weather inducers all die in the process of stopping your sweep, opposing Chlorophyll users have to be faster and not dead already. Really the only things that are actually "potential threats" are Urugamosu, Heatran and bulky Dragonite and if you haven't already dealt with them before trying to sweep that's your problem. Salamence isn't a shit Pokemon because you locked yourself into Outrage without dealing with their Steels beforehand.