Valid interconnection of sources?
Yes, it's valid. The circuit theory rules here are:


Two different ideal voltage sources may not be connected in parallel (across the same pair of nodes).
Two different ideal current sources may not be connected in series (in the same branch).


Neither of those rules is broken, so the combination of sources is valid. The circuit obeys KVL, KCL, and conservation of energy.

Putting two voltage sources in parallel violates KVL -- the sum of the voltages around the loop is not zero. Putting two current sources in series violates KCL -- the sum of the currents entering the node between the sources is not zero.