I'm going to assume that framework = walls and roof.
Generally the official answer is "no", the framework is not meant to bear loads. The upfitters manual generally guides all loads to the floor (example: recommended shelf structure is seated on floor and mounted to wall/pillars for stability). One exception is the roof, which is rated for approx. 300 pound load (I forget exact number, also some minor variability between low and high roof, etc).
But in reality, many DIY conversions utilize the framework to varying degrees. I have 13" segments of L track vertically mounted onto the C and D pillars in my 144" Crew; each is mounted via 3M tape and four or five 1/4" bolts into either rivnuts, or through-bolted to backing plates & nuts. These four tracks together support 450+ pounds of bed platform and sleeping adults. I don't have the slightest concern about the capacity of the pillars to support that load. I'm confident my bed panels would bend/fail long before the support points on the pillars.
I think the conventional wisdom is "OK, within reason" for using the van framework to directly support loads.