In HPLC the compounds are separated before detection. In spectrophotometer they stay together. If you use an indirect method (using reagents) to detect one particular compound at a time the its ok. It will be fine as long as there is no compound having overlapping lambda max. If such scenario occurs then HPLC, LCMS is best for drug.
However, If you want to use gas chromatography then high temperature may degrade the drug (varies with case to case).
You can use Capillary electrophoresis (CE) as well. You can also carry out hplc and CE and then compare the results. Both are differently sensitive methods