While rank 6 seems a bit odd of a long wait for climb, the climb skill really is meant to represent full on expert climbers, not climbing a low wall/very steep slope etc. That is done via a Strength test (and Strength is one of the Guardsman's primary statsmeans they won't be that bad at it). Climbing, as represented by the climb skill, would only really be appropriate for mountain troops or similar, especially in a setting like 40k where troops are normally not as well trained as as first rate professional armies are now (Western WW2 armies is how I see the average, and while those units which were expected to do lots of serious climbing would train extensively in it, your average tommy/jerry/yank would not be expected to be able to climb a sheer cliff unaided). Don't see much of an issue there.
I also don't think basic first aid would be as wide as it would in modern armies. I would say allow a "Combat Medic" background package to include Medicae, but that would probably be about it.
Navigation (Surface) is a bit odd, but then the Imperial Guard is generally a force which doesn't encourage independent action, and so many units would probably even think it best if most soldiers didn't know where they were. That's the officers job, he simply tells his men which direction to go. Now, exceptions would be made for certain odd units and scouts, but your average Grunt's job is to do what the officer tells him, not decide where to go and what to do himself.
The one I genuinely find a bit odd is that Common Lore (Imperial Guard) is a 2nd rank skill. Now, I can understand it not being part of the compulsory starting skills (character may be a total conscript, new to the job, or may just never have absorbed the information from around him, but not having it as an option is plain weird).