I've made a fix to the mssqlnative driver, in order to have the field "is_identity" in the column properties resulting from MetaColumns. This fix required 2 changes in the code: the first at line 114,
var $metaColumnsSQL = # xtype==61 is datetime
(case when c.xusertype=61 then 0 else c.xprec end),
(case when c.xusertype=61 then 0 else c.xscale end),
(case when c.status=128 then 1 else 0 end)
from syscolumns c join systypes t on t.xusertype=c.xusertype join sysobjects o on o.id=c.id where o.name='%s'";
Adding (case when c.status=128 then 1 else 0 end) in order to extract the "is_identity" information.
Then I added the function MetaColumns from ADOConnection and changed it in order to support the new "is_identity" field