I vote no. A vertical ladder just isn't safe compared to a portable extension ladder. An extension ladder should be at an angle based on the 4 to 1 rule - 1 foot out for every 4' in height and should be min. 3' above the roof.
OSHA ladder safety- same in Canada. Falls from ladders are a leading cause of worker injuries from mild to death and doesn't have to be a tall ladder to get seriously injured. Same with homeowners too. I fell off a 6' stepladder 20 years and still have hip pain and can't sleep on one side. I can't imagine how difficult it would be to climb up to the roof on a fixed vertical RV ladder and get yourself over and onto the roof surface - worse going down too. Do RV ladders have an ANSI duty/safety rating or is it from RVIA?
Consider safety first. Use a quality extension ladder. The only time I use ours is for cleaning and putting the cover on which gets done at home. DW works at our workers comp. board (WorksafeBC) and she won't even let me use a step stool without a hardhat and fall restraint. :( Having said the above, a factory ladder on an RV is great for hanging a tote tank, bike. etc. :)