This was local NY fauna?
Oddly northern for G. grisea, but I'm inclined to agree with you Alex. I'm honestly not all that well versed in my mantid nymphs... although I've always wanted to rear some aside from European species that I tend to around the landscaping. Always fun to go out and offer a roach to a wild mantis whose so kindly tended to other garden pests.
We might have a guide to mantodea in the lab, I'll double check and see if I can find anything else about these guys.
As for your frogs - these nymphs should make excellent feeders while they're still in their younger instars. Should take fruit flies and springtails with gusto. Here's a quick caresheet I found by Peter Clausen...a really great guy in the bug community.
Mantis Care Sheet