The antenna is definitely supported, that document is just geared more towards what 1252s are normally used for. As long as the connector is the right type (RP-TNC) and it's meant for the correct band, the antenna will work. There's nothing to look at beyond those two things.
However, I'm not sure that Cisco allows 802.11n data rates to be used in bridge mode. Before purchasing this solution, I would call your Cisco rep to ask this question. And if you find out, please let me know! I'm quite curious. :)
After reading Jeff's post, I got curious too and found this link. Apparently, Cisco TAC doesn't support bridging using the 1250 but a number of posters have successfully implemented it. Here's the link: