Firstly, yes, AF SDK could be used in PI ACE. However, if the data stored in SQL server is updated, PI AF might not know the updating. PI AF will just store the link to PI server and relational database server, but it could just show the updating data in PI, cannot show it in the SQL actually. This should be reason why needs to use PI RDBMS interface to transfer some data from SQL server to PI.
To achive your goal, I think you could link Equipment ID to AF server using "Table Lookup" data reference, I believe this should be stored in SQL server. After this, it is necessary to use some .net function to link the SQL server. Then, for example, Equipment ID in AF server and SQL server could be data matching bridge in you code, and you could this as the search condition to do your function.
Wish this could help you.