My feeling on recalls is that any brand that's large enough is going to have some eventually. Unless a company has a really unusually high number of recalls, what's more important to me is how the recalls happened and how the company conducted themselves. Are many of them voluntary recalls that happen just in case, with very few to no animals getting ill before the issue is caught? Is the company proactive when there's a major event and transparent about what they're doing to fix the problem and improve? What is their attitude towards families that have been impacted by the reason for the recall? Some companies are super proactive and on top of things, others try to deny that there's a problem until the end of time and brush everything possible under the rug, or try to deflect blame onto distributers or even consumers themselves. I'd feel a lot safer with the former rather than the latter.
Not sure which category Diamond falls into as I haven't fed their brands, and they aren't available where I currently live, but I'd look at their responses to the recalls and how many are voluntary vs. mandatory, not just the numbers alone.