Anybody figure out how to use or access the new inventory user defined fields?

To setup these new Inventory fields you must run SM-P-E..  
 
this will let you use MTIC.PROD.SUBST[2 - 5]  each one is 25 characters  and you can specify the Number (mostly for screen position). A Label (text on the screen) What field to store it in ( MKIC.PROD.SUBSTR[2 - 5]) and the starting position and length in that field. once you have that filled in, then T7INA and T7INB will have a new tab called User Defined.

BTW - is it safe to assume that the new fields are only visible and usable in the EVO version of T7INA and not in the DBA version of T7INA?

Where are you seeing Location number?  There is UDF Number, UDF Label, Inventory Field, Start Pos, and Length.
 
UDF Number controls the Screen Position, UDF label is the Name you want to give it on the screen (and yes it is limited to something like 10 chars) , Inventory field can de MITC.PROD.SUBST[2], [3], [4], or [5] , start pos is from 1 to 25, and length can be 1 to 25.
 
 
Seeing as this is a new feature it is only on the Tabbed views of T7INB and T7INA.
 

example :  MITC.PROD.SUBST[2]    it is alphanumeric size 25.   1234567890123456789012345
                                                                                             test    fred     Bubba  junk 180
 
 
So in the above i have 5 UDF fields   udf1  label= 'TYPE'  Start pos = 1 leng = 5   value in this example is 'test '
                                                    udf2  label= 'Name' start pos = 6 leng = 6   value in this example is 'fred  '
                                                    udf3  label= 'Ref'    start pos = 13 leng = 6  value "            "           'Bubba '
                                                     
 
if start pos were all 1 then when the data was saved,  they would all write to the same place and the last one to save would erase the previous ones.   so in the example above if all had start pos 1  the field MITC.PROD.SUBST[2] would look like this in maintain database
                                                    1234567890123456789012345
                                                   180ka  
 
 as it was saved it would have been test
                                                   fred
                                                   Bubba
                                                   junka
                                                   180ka