Yes, adipex or any other diet pill is an amphetamine, just as Adderall is an amphetamine.
Amphetamine is all that is tested for, so no your doc will not know you have taken Adderall.
The only way he would if was to send off for a 16 panel breakdown to identify exactly which one but he wouldn't do that considering he's prescribing you diet pills he's just testing to make sure amphetamines are in your system due to law requirements.