Interesting. Host and guest are etymologically related, but come from Proto-Indo-European gʰóspot- (“master of guests”), from gʰóstis (“stranger, guest, enemy”) and *pótis (“owner, master, host, husband”) and the other host (army term or inventory) comes from hostis, although that in itself is derived from above ghostis.
While enemy comes from Latin inimīcus, from in- (“not”) + amīcus (“friend”).
Yes, both hospes, hospitis , m., the guest/host word, and hostis, hostis , m., the enemy word, are both ultimately related to each other in the meaning "foreigner, stranger." A stranger/outsider meaning, potentially, both someone that you make special provision for entertaining (under the heading of "diplomacy," as it were), and also someone whom you have to resist, because his interests may be opposed to yours. Interesting; and English "guest" is etymologically related, too (all info from the Oxford Latin Dictionary).