SQL Server 2012 Exclude a value
If my understanding of your question is correct and you are only wanting to return records from tbloffer if there are also records in tblRecord matching those buyer ids, then you should be able to add a clause within your join so that it will only return those records.

I think this will cover it for you.

SELECT  COUNT(DISTINCT r.RecordID) AS Lines
      , COUNT(r.RecordID) AS Offers
      , MONTH(r1.Submitdate) AS M
      , DAY(r1.submitdate) AS D
FROM    tblReq r1
        INNER JOIN tblRecord r
            ON r1.ReqID = r.ReqID
        INNER JOIN tblOffer o
            ON r.RecordID = o.RecordID
            AND r.BuyerID = o.InsertedID
WHERE   r.BuyerID IN (36, 160499)
        AND o.OfferTypeID IN (1, 3)
        AND r1.Submitted = 1
        AND r1.SubmitDate &gt;= '2015-07-01'
GROUP BY MONTH(r1.Submitdate)
      , DAY(r1.submitdate);


Hopefully I am understanding your question correctly and this is able to help you.