You can use a Union.
This will return the results of the queries in separate rows.
First you must make sure that both queries return identical columns.
Then you can do :
SELECT tableA.Id, tableA.Name, [tableB].Username AS Owner, [tableB].ImageUrl, [tableB].CompanyImageUrl, COUNT(tableD.UserId) AS Number
FROM tableD
RIGHT OUTER JOIN [tableB]
INNER JOIN tableA ON [tableB].Id = tableA.Owner ON tableD.tableAId = tableA.Id
GROUP BY tableA.Name, [tableB].Username, [tableB].ImageUrl, [tableB].CompanyImageUrl
UNION
SELECT tableA.Id, tableA.Name, '' AS Owner, '' AS ImageUrl, '' AS CompanyImageUrl, COUNT([tableC].Id) AS Number
FROM
[tableC]
RIGHT OUTER JOIN tableA ON [tableC].tableAId = tableA.Id GROUP BY tableA.Id, tableA.Name
As has been mentioned, both queries return quite different data. You would probably only want to do this if both queries return data that could be considered similar.
SO
You can use a Join
If there is some data that is shared between the two queries. This will put the results of both queries into a single row joined by the id, which is probably more what you want to be doing here...
You could do :
SELECT tableA.Id, tableA.Name, [tableB].Username AS Owner, [tableB].ImageUrl, [tableB].CompanyImageUrl, COUNT(tableD.UserId) AS NumberOfUsers, query2.NumberOfPlans
FROM tableD
RIGHT OUTER JOIN [tableB]
INNER JOIN tableA ON [tableB].Id = tableA.Owner ON tableD.tableAId = tableA.Id
INNER JOIN
(SELECT tableA.Id, COUNT([tableC].Id) AS NumberOfPlans
FROM [tableC]
RIGHT OUTER JOIN tableA ON [tableC].tableAId = tableA.Id
GROUP BY tableA.Id, tableA.Name) AS query2
ON query2.Id = tableA.Id
GROUP BY tableA.Name, [tableB].Username, [tableB].ImageUrl, [tableB].CompanyImageUrl