Castrol is essentially what Triumph puts in my twins and triples. Seems to do the job and I suspect most of their triples put way more stress on the oil than the 1330 Rotax. The Rotax being dry sump-ed will have a much greater oil capacity, less problems with oil starvation with sideways g-forces on cornering, and a more constant oil temperature. So, anything truly fully synthetic, approved for wet clutch systems and endorsed by a name brand motorcycle manufacturer who "recommends" 10,000 mile oil change intervals is highly unlikely to cause a 1330 Rotax to grenade due to oil related failures with 5,000 mile oil and filter changes. With a 7,000 rpm rev ceiling and producing 115 bhp out of 1330 cc it is hardly the same stress on the oil as Triumph 1200 triples producing well over 150 bhp at 10,000 plus rpm.
If you change your oil regularly, more often if you abuse the red-line or live in a severe heat, cold and/or high dust climate, any choice of the major independent oil brands, or those of the big 6 motorcycle manufacturers will be just fine. I'm not going to lose sleep over which exact brand of high quality oil sits in the sump of my Spyder or motorcycles, or cars for that matter. I'm sure they are not all quite the same and have their own brand specific advantages and disadvantages, and differing prices too, but I think the vast majority of any quality brands are up to the task. I suspect any name brand oil with 5, 10 or even 15 W40 rating will work fine as they all run to the 40 rating when warmed up. If you live in Arizona or the likes I'm sure 20w50 will be just fine too.
If Triumph changed their oil supplier from Castrol tomorrow, I wouldn't worry about it in the least. Same goes if Can Am changed their supplier for XPS. I think it makes about as much difference as filling street tires with air or nitrogen, to be honest.