Since its almost impossible for a commish to rule on 'intent', I think that this is a little more complex than some of the above 'higher ground' opinions. Don't get me wrong, I always try to err on the side of unquestionable ethics.
However, if he comes to the same roster moves saying:
"I've got a bench guy or two who is expendable and won't play unless I have injuries. Valverde is available and insurance for my closers is more important than for my 5th starter. I will pick up Valverde and if someone more valuable to my roster is available later, I'll change him out."
The moves would be identical and I don't think that anyone could question the transactions.
I don't necessarily think its right to pick up players that you don't intend to use. However, without roster limits, the team is better off with Valverde right now. I say make the move. Who knows... Izzy could pull up lame after his next pitch.
Blessed are the cheesemakers.