RE: Reverse Engineering. . . I would take this to mean that you don’t use the model as a blueprint for fabricating, developing, manufacturing, or engineering purposes… in such a way that it supplies information towards the means of making a direct copy of the original product/design. (…as a real world object/product).
Hence the clause of needing to obtaining the ‘source material’ directly from the developer… before doing so.
RE: Impermissible Aggregation… and ones use of the model in their own publication. . . can lead (or be misconstrued) as that person claiming, or attempting (even accidental) ownership for that which is not theirs (in terms of intellectual property rights). Obtaining approval and permission from each developer will likely mean that you’ll need to agree to provide proper credit before they’ll allow it’s use. (maybe other conditions come into play as well). Requiring this permission also protects Trimble (SketchUp/3D Warehouse) to some degree in that they can’t be blamed for unauthorized use of a model—since you’re taking responsible for properly obtaining all of the permissions yourself by agreeing to the terms and conditions of the 3D Warehouse.
Royalty Free is the condition of not collecting money, or paying license fees for the models use… but that doesn’t detract from the protection of copyright, or intellectual property which the model developer still has… and which are protected by the first set of of your questions which deal with obtaining permissions for use.
Am I lawyer?.. NO
Is a member of my family a lawyer?.. NO
Would any judge on the planet ever call me up to discuss legal implications of a contract?.. NO
Would they be impressed if anyone sites me as a source for legal information?.. NO
Do I hope my comments are still useful anyhow?.. Yes, More or Less. . . you’ll be wise to continue this search further… and I’ll be happy to stand corrected where need be.