Nutty. I react to dog scratches like that, well like most people do, I don't think he and the dog have been in the same room at all today. She's been too busy trying to scare off the snow by barking at it 
I've been coming up in similar weals since an allergic reaction to anti-biotics recently. Mine are smaller though, and itchy. When I scratch I get the weals. So maybe an allergic reaction? Or maybe he scratched himself post snow ,as skin can itch when warming up, but didn't register it as he was cold and numb, so scratched quite deeply?
ok read your post again, hadn't absorbed the "shoving it down collars" bit. I think the marks are the nails of the shover, <adjusts deerstalker, puffs pipe> not felt at the time due to the numbing effects of snow.
Interesting theory. I saw the shoving whilst giggling and it was a collar pull and dump, but I can check with the perpetrator as he is ds's best mate and lovely.
I have personally shoved snow down the back of several necks, and my arm tended to reach down as far as is humanly possible ,like a plunger, for maximum effect.
<smugly convinced of the rightness of my theory>
Ds was still awake, he has confirmed that snow entered by a snowball being slapped on his lower exposed neck.
He is also now enamoured with Zombie, and thinks she's great.
Well know more have appeared. Checked with school, area where they were playing hadn't yet been gritted.
We are now speculating snow burn 
Thats really odd!
No chance of coming into contact with fiberglass? like the fluffy sort you put in lofts?
Ive seen similar cut marks from that before.
A cat or dog that sleeps on his bed?
Interestingly, my son woke up with similar on his face. I thought it was Impetigo, but GP says it's not, but I have cream.
See?
OMG, it's infected Tee's son through the internet.
I know I know! It's a computer virus <collapses in giggles at own wit>
The other side of his face looks even more like it's been scratched.
I laughed, Poledra!
Tee 
That's weird.
Omg this is how the zombie apocalypse starts. Actually on Mumsnet.
But seriously, how freaky, that's exactly like ds 
Only humans on beds here and no feather pillows. Ds's definitely occurred at school at some point.
Are any of the dc wearing gingham dresses and carrying Mr Flibble? <hopes someone gets this reference>
<<bloody red dwarfers>> 
<<oh fuck outed self>>
Mine still has a very low grade fever. Does yours Honey?
Nope, he is a picture of health. [apart from the erupting welts of mystery]
So more have erupted? We seem to be holding steady on the face. And the fever.
I'm never going to get any work done...
I don't think it's actually more, just as they've tried out they've become redder so it looks more.
Ds is thrilled he has spread. 
Well, mine now seems to be 100% better...