I work in welfare rights advice and I have complicated feelings on this subject.
I've never worked in the DWP but I've dealt with them enough to get an idea of what it might be like and I've worked alongside people who have worked for them.
Welfare rights officers tend to be on quite short contracts and are often looking for work. The possibility of working for the DWP has certainly occured to me as a safety option, since I obviously have some transferable skills.
Some of the current problems within the DWP are to do with understaffing. So I'm pleased to see that they are recruiting.
As PP have said, a lot of the problems people experiance with their benefits are to do with the system not running efficiently or decisions not being made quickly enough. If your job involves sorting this stuff out then you will be on the side of the angels much of the time....
Having said all that:
My current job involves fighting the claimants corner and utilising all the arguments possible bring their particular situation within the qualifying critieria.
I'm aware that if I was a DWP decision maker, i would be expected to tread a much more conservative line, making decisions within the guidance. I personally would enjoy that less.
I would also not enjoy being the person who actually has to refuse a claim (although im often the person who has to advise someone that their claim is likley to be refused- so perhaps its a narrow distinction).
I would certainly have a very hard time being the decision maker that decides on sanctions. I think that is a job I would genuinely be unable to carry out on moral grounds.
As PP have said: Its likely that you would lose your sympathy for claimants over time. Partly because you might have to experiance said claimants ringing you up in a distressed state and shouting at you. Partly because cognitive dissonance will tend to lead you to justify the stuff you have to do.
If that doesn't happen and you find yourself with genuine moral scruples a few months in, you could always take your working knowledge of the benefits system and cross over into advocay or welfare rights.
I hope this helps OP and good luck with whatever you decide to do.