Correct. The Galaxy S3 uses either its Qualcomm MSM8960 SoC or an outboard Broadcom solution for GNSS. Regardless, both Qualcomm and Broadcom support GLONASS, as does the S3. And GLONASS likely does not require an additional antenna, as it operates ~1600 MHz, very similar to GPS in that regard.
This app -- in its free version, paid version, or both -- displays GLONASS satellites.
https://play.google.com/store/apps/details?id=com.chartcross.gpstest
Note, however, that GLONASS may be used only for backup. Hence, if you have sufficient GPS satellites "in view," then GLONASS may not be used.
AJ