Jaguar Knights? It obviously ties in with the Jaguar Warriors of the Aztecs while retaining the element of knighthood we're working with. Mayhaps the name could represent their style of warfare, sudden suprise strikes from mounted warriors.
Aztec culture also involved worship of the sun, and based off my (rudimentary) knowledge of germanic tribes, druidism could be involved. So maybe a name like the Verdant Suns could be used. Or we could appeal more to the heavy infantry approach and call them the Breacher Legion or something like that.
I think we could have a very good basis for a chapter focused on boarding action. Other names off the top of my head to fit with that are:
Heart Rippers (going into ships and ripping out the 'heart' by disabling power or capturing the captain)
[Insert Adjective] Privateers
The name doesn't really have to tie into the chapter I suppose, so it could likely be that they become something like the Disciples of Macragge. But names can invoke great imagery. With the Black Templar, we know that they're zealots and spread their faith to all corners of the galaxy. The Salamanders are masters of flamecraft, likened to the great drakes of Nocturne. Even the Ultramarines name tells of what they are about, modern day marines adhere by a set of "rules" on how conflict should be handled, the warriors of Macragge take this to the next step and have a solution to ALL conflicts, and diverging from these solution means that failure is a likely result for them.
If that made no sense, then ignore me!
But for me, names that help to paint an image of what a chapter is like goes a long way in giving a chapter personality.