Yes, simply join t_attributeTag multiple times, set the join property to a fixed value in the join condition.
select att.Name, att.Type, att.[Default] as 'Value'
, tv1.VALUE as Tag1, tv2.VALUE as Tag2
, att.Notes as Notes
From t_attribute att
left join t_attributetag tv1 on att.ID= tv1.ElementID
and tv1.Property = 'Tag1'
left join t_attributetag tv2 on att.ID = tv2.ElementID
and tv2.Property = 'Tag2'
inner join t_object on att.Object_ID = t_object.Object_ID
where att.Object_ID = #OBJECTID#
Geert