I started a new Relentless Assault fort, and finally got frogmen first! A siege of one unit came in early Summer, eliminating my Dwarven caravan, unfortunately. At first I overestimated the strength of the frogmen and tried to use my Mechanic to quickly lay some more traps -- he only got one built in time, though, and because he was cut off from the rest of my Dwarves he was overrun in the fray and killed.
I had drafted the other six and set them up behind a bottleneck. The frogmen split into two or three groups chasing my animals (4 of 5 which they eventually killed). I used my squad of 6 (two with picks, one with an axe) to kill first a group of 3 frogmen that hadn't broken off, and then to pursue a squad of 6 that had wandered south while the rest went north. My wrestlers suffered no deaths but one casualty against the group of 6, and with 9 frogs dead the remainder fled the map.
I assume that I was so victorious because frogmen would be small, even compared to my dwarves. Some of them were macefrogs, and those were the ones that gave one of my dwarves a mangled led.
It was pretty awesome and a good challenge to have to deal with a siege this early, especially one that means I won't be seeing a caravan until Winter and I won't be able to set up a trade agreement with the Dwarves until next year, much less get what I need (2 Summers into the future). Like I said earlier, this was the first time I actually got frogmen ... normally I jump straight to lizardmen, which have been much harder to deal with.
The lizardmen and frogmen are both pretty cowardly though, and now I'll set up enough traps so that their casualties will cause them to flee before I encounter them in melee combat. I can't really afford to risk any more dwarves at this point until I get migrants!
... but, of course, the one Dwarf that got killed was my Mechanic! So it'll take some time to get myself protected, which will hopefully lead to Fun. Again, great mod. It has become my favorite "add more enemies" mod. Thanks a billion!
EDIT: For anyone who is curious, I had about 12,000 dwarfbucks as created wealth when the frogmen attacked me on Early Spring 16. Just in case you want to know what numbers to avoid.