So as far as I can tell, you have gotten wrong information there... I wonder where this information is coming from? As a frequent buyer on the asset store I can tell you, 100% of the assets I bought imported fine (even though not 100% of them were really good in the end, but that is a different story ). I am pretty sure not all of these devs paid for the pro version of Unity, why would they if they make less than 100k$ a year selling assets (don't even know if selling assets is included in the 100k$) and do not need the pro only tools (though the profiler can certainly be useful)?
EDIT: Oh, I forgot... as you might have guessed from the text above, I have a pro license.
I did some quick googleing around, and it does look like I have had some misunderstandings with the Unity asset stores policies. If I understand correctly, if the thing sold in asset store can be imported into the project, such as sounds, models etc. then it doesn't matter if you are using free or pro version, but if you export something out of unity and then sell the stuff, you cannot mix free and pro version things? Like if something is being made with free unity, like unitypack or whatever, then being put on asset store, this cannot be used in pro version and vice versa? I guess I still might have misunderstood something.
How would something like scripts count as? You can make scripts on any text editor, but they are kind of unity specific things still. I suppose they would be just considered non-unity property.
As for free version, with Unity5 free version does include profiler as well, so you can use even profiler with free Unity nowadays.