Yes, both Worklow and Forms are using the same account for access.  The difference is in Forms, i have the option to choose a stored procedure and in Workflow I am not seeing that.

Here is the Forms lookups using that stored procedure (Bottom Image).  I can see that stored procedure in the dropdown for Query Data Activity.  I tried putting the stored procedure in a Custom Query Activity and it always returns -1 row(s) affected.

Here is the custom query 

ALTER PROCEDURE [dbo].[Ad_Name_Results] 
	-- Add the parameters for the stored procedure here
	@employee nvarchar(30)
AS
BEGIN
	-- SET NOCOUNT ON added to prevent extra result sets from
	-- interfering with SELECT statements.
	SET NOCOUNT ON;

    -- Insert statements for procedure here
SELECT displayname As Employee, SUBSTRING(manager,4,(CHARINDEX(CHAR(44),manager,1)-4)) As Manager, mail as Email, Department, SUBSTRING(company,1,(CHARINDEX(CHAR(124),company,1)-1)) As EmployeeNumber, userPrincipalName as Username, 'MVIUSA\'+sAMAccountName as UserLogin, SUBSTRING(company,(CHARINDEX(CHAR(124),company,1)+1),(LEN(company)-(CHARINDEX(CHAR(124),company,1)+1))) As PayrollFolder
FROM OpenQuery ( 
	ADSI,  
	'SELECT displayname, mail,  manager, department, company, userPrincipalName, sAMAccountName FROM ''LDAP://WS16-DC1/OU=MVi User Accounts, DC=mviusa,DC=local'' WHERE objectCategory = ''Person'' AND objectClass = ''User'' ')
	WHERE displayname = @employee  ORDER BY displayname
END