SQL Data Warehouse - Is it possible to switch a whole table to a partition? Probably a stupid question, but I wanted to know if it was possible to switch a whole table into a partition of a larger table?

I'm guessing not, as check constraints aren't available to constrain the table on the partition boundary.
Azure SQL Data Warehouse does not support check constraints so partition switching is a slightly different ballgame.  The partition scheme as described in the table DDL (rather than a partition schema/function pair) must match exactly in both tables.

Code example duplicated from here:

-- Assume we have a file with the values 1 to 100 in it.

-- Create an external table over it; will have all records in
IF NOT EXISTS ( SELECT * FROM sys.schemas WHERE name = 'ext' )
EXEC ( 'CREATE SCHEMA ext' )
GO


-- DROP EXTERNAL TABLE ext.numbers
IF NOT EXISTS ( SELECT * FROM sys.external_tables WHERE object_id = OBJECT_ID('ext.numbers') )
CREATE EXTERNAL TABLE ext.numbers (
    number          INT             NOT NULL
    )
WITH (
    LOCATION = 'numbers.csv',
    DATA_SOURCE = eds_yourDataSource, 
    FILE_FORMAT = ff_csv
);
GO

-- Create a partitioned, internal table with the records 1 to 50
IF OBJECT_ID('dbo.numbers') IS NOT NULL DROP TABLE dbo.numbers

CREATE TABLE dbo.numbers
WITH (
    DISTRIBUTION = ROUND_ROBIN,
    CLUSTERED INDEX ( number ), 
    PARTITION ( number RANGE LEFT FOR VALUES ( 50, 100, 150, 200 ) )
    )
AS 
SELECT * 
FROM ext.numbers
WHERE number Between 1 And 50;
GO

-- DBCC PDW_SHOWPARTITIONSTATS ('dbo.numbers')


-- CTAS the second half of the external table, records 51-100 into an internal one.
-- As check contraints are not available in SQL Data Warehouse, ensure the switch table
-- uses the same scheme as the original table.
IF OBJECT_ID('dbo.numbers_part2') IS NOT NULL DROP TABLE dbo.numbers_part2

CREATE TABLE dbo.numbers_part2
WITH (
    DISTRIBUTION = ROUND_ROBIN,
    CLUSTERED INDEX ( number ),
    PARTITION ( number RANGE LEFT FOR VALUES ( 50, 100, 150, 200 ) )
    )
AS 
SELECT *
FROM ext.numbers
WHERE number &gt; 50
GO


-- Partition switch it into the original table
ALTER TABLE dbo.numbers_part2 SWITCH PARTITION 2 TO dbo.numbers PARTITION 2;


SELECT *
FROM dbo.numbers
ORDER BY 1;


HTH