Excise Invoice...

Excise regd dealer should be issue Excise invoice only for all dealer either registered or unregistered

a registered dealar can issue cenvatable invoice irrespective of whether purcheser is registered dealer or not.

but one thing here to note that the unregistered dealer cannot distribute further credit of duty paid by him by issuing a cenvetable invoice. 

Yes, A registered dealer can issue excisable invoice to unregistered dealer.