If you mean to suggest there'd be the same risks as China, consider that Vietnam has consistently kept a certain distance to China, and have shared concerns with the US over Chinese expansionism. They're not particularly ideologically close, and politically there are few potential situations where deteriorating relationships between the US and China will negatively affect US-Vietnam relations, and some where it might improve them (e.g. if the issues in the South China sea escalates).
Apple already has a growing iPhone assembly base in India, which is set to go to 25% of its total iPhone production within a few years. While Apple is still looking for low cost production, I’m sure it doesn’t want a repeat of China by concentrating a lot on one or two countries. I think the current moves are a temporary aberration, since concentrating iPhones in India, iPads and Macs in Vietnam and so on doesn’t diversify the risk as much as ensuring that every product is assembled in more than one country. I’m sure Tim Cook is spending a lot of time working on such measures to de-risk manufacturing and maintaining the company’s profit margins.
All the countries that support low cost assembly and manufacturing in Asia have different kinds of problems as far as governments, policies and stability are concerned. Apple or any other company has to figure out the right mix and plans.
If you've ever spent any time in Vietnam, you'd understand that.