I'm nowhere near ready to move on to assignment 2. But even from what I've done for assignment 1 leads me to believe that we can.
I'm busy looking at PDA's in Chapter 14/15, and they don't seem to have any reject states anymore. I suppose it all depends on whether you want your string to crash or to be rejected, and seeing that they haven't introduced consequences for strings crashing I'd say that at the moment both outcomes are the same.
Found your answer: Page 327
A PDA is in conversion form if it meets all the following conditions:
1. There is only one ACCEPT state.
2. There are no REJECT states.
And CFG is for context-free languages which is handled in Chapter 17 where our PDA questions comes from.
You don't need to add REJECT states to a PDA for it to be a valid PDA. If the PDA gets to a point where it cannot proceed and don't have a REJECT state to go to, the "program" crashes. It says so in the book (can't find the reference now).