Yes, you can distinguish them. As ericoid mycorrhizas are formed mainly by ascomicetous fungi, their hypha are septate, on the other hand arbuscular mycorrhias are produced by glomeromycotan fungi which produce aseptate hypha. So based on the presence/absence of septa that would indicate you which kind of fungi, and hence mycorrhiza, it is. However, other kind of soil fungi also produce septate and aseptate hypha, so maybe the main problem would be to discriminate against those fungi and not to include them in mycorrhizal fungi. 

Regards!