Yep, sure is. Stims fire up your sympathetic nervous system (fight or flight mechanism) which has two parts - alpha adrenergic and beta adrenergic. Alpha is mainly involved in vasoconstriction, amongst other things, where as beta is involved in your heart rate/force (also dilating airways in your lungs). Beta blockers only knock out the beta part, so they slow your heart down but leave unopposed alpha arenergic stimulation which can lead to severe vasoconstriction. As blood flow is reduced (heart slowed and beating less forcefully) this means blood can have difficulty getting to the tissues eg limbs and heart (which can cause a heart attack). It's not a good idea to combine them an you wouldn't be given them in hospital for a stim overdose unless under very controlled conditions, or a combined alpha and beta blocker was used.
As an aside, the reason many asthmatics can't take beta blockers is beta adrenergic stimulation dilates your airways; beta blockers (especially non cardioselective ones like propranolol) can constrict them, triggering an attack,
/science lesson :D
Morning guise, I'm just passing through..