Can I assume that terrain clearance is guaranteed as I am following the G/S?
Affirm.
the check altitudes, on the other hand, will be affected by the temperature, and I will expect to cross them lower than mentioned on the chart, even if I am on the G/S?
When on the glide slope your Altimeter will show that you are apparently higher than the check Altitudes.
You have to raise your DA i.a.w. your published tables.