Based on MId year 2010 MBP - yes.
I've got a 500 GB internal SSD drive with OS X Lion and and a shaved 5 gb drive as a Lion Bootable/Restore disk with disk utility.
I picked up the Wintec Filemate 96GB SSD card and installed it with two partitions, 45 GB for Boot Camp with Windows 7 (bootable) and 1 partition for Data 45 GB - accessible by both the OS X partition and the Boot Camp partition.
Doing this - The Boot Camp drive with Windows 7, is formatted in NTFS and the 2nd partition is formatted in HFS+ which both the NTFS and OS X Lion will read and write to.
THere are a ton of articles out there about boot camp and external drives not working, I'd guess this one counts as a 2nd internal drive due to the cards ESata connection. It's nice. Both drives are SSD, and both windows and OS X are really fast. Holding Option key allows booting into Boot camp to launch either Mac OS X or Windows.