Or on offensive SubPetaya sets? Speaking of which, is Sub Petaya even viable on Urugamoth? It does resist Bullet Punch and Mach Punch, and there's not much that it can't switch in and setup on(and the SR weakness in this case may even be helpful in some cases). Aqua Jet hurts though.
Um, I'd still go for Swarm on normal BD sets because of the power boost gained after switching into SR+taking an attack. Just my opinion though, Flame Body never worked for me really.
I used a SubPetaya Ulgamoth once, and it won me a fair few matches (may have been mentioned already, but...):
-Fire Blast
-Bug Buzz
-Substitute
-Butterfly Dance
Nature: Timid
EVs: 252 SpA/4 SpD/252 Spe
Item: Petaya Berry
Ability: Swarm
You shouldn't be fighting against a Blissey with Urgamosu unless you're at about +6, Toxic Spikes are down and it doesn't have Aromatherapy, or you're running LOLphysicalMoth.
Speaking of physical Ulgamoth, it has a fair few options, but it doesn't have the raw base Attack to use them. Here's a (hypothetical) physical set if its Attack was a bit higher:
-Flare Blitz
-Wild Charge
-Zen Headbutt/Double-Edge
-Bug Bite/Double-Edge
Nature: Adamant
EVs: 4 HP/252 Atk/252 Spe
Item: Life Orb/Choice Band
The above set is pure novelty, and not to be taken seriously.