This article is from the Asthma FAQ, by Patricia Wrean and Marie Goldenberg email@example.com with numerous contributions by others.
Yes. Quoting from the Product Information Sheet that comes
with the Serevent (salmeterol) inhaler, manufactured by
Allen & Hanburys:
"Serevent Inhalation Aerosol should not be used more frequently
than twice daily (morning and evening) at the recommend dose.
When prescribing Serevent Inhalation Aerosol, patients must be
provided with a short-acting, inhaled beta2-agonist
(e.g., albuterol) for treatment of symptoms that occur despite
regular twice-daily (morning and evening) use of Serevent."
"When patients begin treatment with Serevent Inhalation Aerosol,
those who have been taking short-acting, inhaled beta2-agonists
on a regular daily basis should be advised to discontinue their
regular daily-dosing regimen and should be clearly instructed to
use short-acting, inhaled beta2-agonists only for symptomatic
relief if they develop asthma symptoms while taking Serevent
"The safety of concomitant use of more than eight inhalations per
day of short-acting beta2-agonists with Serevent Inhalation
Aerosol has not been established."
So the above quotes seem to imply that it is okay for asthmatics
taking Serevent regularly to also use Ventolin (albuterol) as
needed, provided one doesn't need it too often.