Under File > Insert (in LayOut), you can insert any "insertable" file type including skp files (other than the one you "started" your LO file with when sending it straight from SU).
Here you can also insert rtf files - note that this seems to be more efficient than typing in text straight into LO as these files will be stored inside the *.layout file separately and if something goes wrong, it is always easier to recover.
As for skp files (either "sent" to LO or "inserted" later), this is a very important advice:
@cmd said:
TIP - you may want to establish all the views you want to display in SketchUp first through Scenes. Once the model is in LO, you have access to all the scenes assigned to your SketchUp model.
I.e. make sure that you create your scenes first, update them every time you make a change and also always update the assigned style in SU. These (scenes and styles) can be set in LO and unless you have previously set them up in SU, you will have issues.
Think this way; what a scene in SU is, the same thing a page in LO is (in fact, before SU 6 came out with the first version of LO Beta, scenes in SU were called pages). Now a "scene" is mostly referred to a camera view (and a bunch of other settings of course) in 3D SU while a "page" is mostly referred to its 2D ("to be printed on pages/sheets") counterpart in LO.