I have to agree with your DH. That's how I pronounce both spellings also.
Me too, I'd pronounce them the way he says. I also see Ariel as more masculine, despite the Little Mermaid connection (which might be good to distinguish your daughter from anyways?), because of the character in the Tempest and I know a male named Ariel.
So even with the "elle" trendiness, I'd actually agree with your DH go with Arielle, especially if that's the way you want it pronounced. It is a really pretty name and isn't one of the more popular or widely used "elle" names.