Code:
(setq dDbx (vla-getinterfaceobject (vlax-get-acad-object) (strcat "ObjectDBX.AxDbDocument." (substr (getvar 'acadver) 1 2)))
cFile (getvar "c:\\where is your block. dwg"
)
(vla-open dDbx cFile)
(vlax-for block (vla-get-ModelSpace dDbx)
(progn
(if (vlax-property-available-p block 'ObjectName)
(if (equal (vla-get-ObjectName block) "AcDbBlockReference")
(print (vla-get-Units block)); or (vla-get-Unit block); etc
)
)
)
)
(vlax-release-object dDbx)
I did not test here. But with something in this line you will be able to get the unit from a block before inserting into your drawing. I did not quite understand your doubt!
Sorry about my English. I'm in Brazil!