Part time work while on VTOS course

What is the position regarding doing part time work when a person is on a two year vtos course.If this work compliments the course been followed and consists of a number of hours a month.
Can a person do this work and continue to finish the two year course.
I assume they will have to sign off on the days they are working but can the two be combined .

Surely they are not 'signing on' for JB/JA while on the VTOS course but, rather, being paid an allowance? You can work and still get VTOS payment.