Both my DCs are Nordic nappers, but then they're half Nordic :) when DS was little, we lived in England and I used to sit outside with him (had shared access and other issues with safety in the back garden).
Like Honeytea, I did worry about the "being in the same room for the first 6 months" so although DD was born over here, I've sat outside with her too (no safety issues otherwise, we live out in the country) when she was under 6 mos. In fact, I still do sometimes, nice to sit and read outside. 
Don't see why this has anything to do with CC... If they're not asleep by the time they're dressed (it's a bit of a process...) then they fall asleep within minutes of jiggling the pram or walking around - if I feel like it, I combine naptime with a workout and take them for a walk.
They do sleep longer outside, not sure about the virus-resistance, but I'm sure they're not MORE ill for sleeping outside IYSWIM.
Whoever worried about the babies being cold - really, really not an issue: they wear thermal underwear, a woolly layer (like a knitted sleepsuit), a snowsuit and a sleepingbag. If anything, I worry about DD getting too hot!
MIL thinks it's neglect though, and tells us birds might go for their eyes etc... 
Also, whoever said the babies must be cold: