Thunderbolt speed via bootcamp?
Since the Thunderbolt drives can run 10 up to 20 Gbps that is much faster than the internal drive in many cases.

I do not see a problem, but can not speak for the boot camp it self.

Here are some numbers:

SSDs itself will have the same speed of reading and writing no matter the cable. The TYPE of cable/connection decides if it can sustain that speed, and this is equally true with USB 3.0, eSATA (v2/3) and TB1/2 - all of them have wide enough bandwidth to support high-speed transfer rates that SSDs are capable of.

USB 3.0 up to 5 Gbits/s (525 MB/s)

eSATA 2 up to 3 Gbits/s (300 MB/s)

eSATA 3 up to 6 Gbits/s (600 MB/s)

TB1 up to 10 Gbits/s per channel (1050 MB/s)

TB2 up to 20 Gbits/s aggregated channels (2100 MB/s)

In summary, those numbers would say the Boot camp would run as fast or faster via Thunderbolt cable to SSD drive.