i have asthma, and have been prescribed albuterol since i was 10 years old. your friend will definitely NOT need his inhaler while taking clenbuterol, as it serves the same function, albeit not in the acute manner that albuterol does. clenbuterol is used as a preventative measure against asthma, where albuterol is most commonly used to treat acute instances. (although i for many years used my inhaler prior to exercising per my doctor's instructions... anyways you get my drift)
what i did notice however was that upon cessation of clenbuterol (2 weeks on, 2 weeks off) i could definitely feel a tightness in my chest, and if i was suffering from allergies at the time it would be necessary to use my inhaler here and there.
so your friend just nneds to keep an inhaler handy, which they should be doing anyways if they have asthma.