Symbols are provided for all of the default environments - block schematic, rack layout, panel layout and pictorial schematic - but not, currently, for a 'blueprint' or 'plan' view.You can create new symbols from existing DWG or DXF files, which I understand Visio can export. To create the symbol simply select File | Open and open the DXG or DXF file. Once opened, select the objects you want to use as your new symbol, drag them into the Library List under My Libraries and type in a name for the symbol. Note that you can create/rename/delete folders under My Libraries by rightclicking.
I hope this is helpful.