At base, HP Lovecraft’s fictional cosmic gods, the Old Ones, et. al., are not gods at all. They are powerful cosmic entities, a few of which might even have been responsible for the origins of Earth, life, and humankind, but who (which?) are in reality “merely” (!) old, powerful creatures – and Creators – but not divinities in the true religious sense.
HPL was able to stay true to his atheistic materialism in even the most fantastic of his tales. He knew that his “gods” were really aliens, even if they normally dwelled transcosmically, in other dimensions, in other times, in areas of space wherein different laws apply than in the space that humans know.
In a stroke of brilliance, HPL managed to (in most cases) attach an authentic-looking-and-sounding liturgical language not to his aliens per se, but rather to the aliens as seen by most of the humans who encountered them over the eons.
“Primitive” human beings were not capable of recognizing the Lovecraftian creatures as aliens or interdimensionals; therefore they tended to interpret them as gods and demons. In this, they were sometimes helped by the aliens themselves, who drew some kind of occult power or even enjoyment from worship by human beings. Moreover, some of these very spells were inspired by these aliens themselves, who encoded or seeded the ancient “scriptures” with certain key phrases and ritual actions designed to assist them and/or to open portals for them onto “the Earth plane”. They saw an undeveloped species, knew its weakness for surrender to a dominating and frightful authority, and took as much advantage of that flaw as they possibly could.
Thus, in all of HPL’s “liturgical” texts in which his aliens are worshiped, there is first of all a striking element of idolatry. By design and by human default, HPL’s aliens are not gods, and so true worship cannot be directed to them. Granted, beings who worship the aliens are not aware that their worship is misdirected, but this does not change the fact that it is false worship, and therefore idolatrous.
Of course, HPL himself would not have seen such worship as idolatrous, because for him there was no God to be worshiped. However, instead of seeing such worship as idolatrous, HPL would likely view it as plain old superstition, part and parcel of all of humankind’s other mistaken forms of (say) nature-totemic worship, which according to HPL’s own perspective, had been thoroughly invalidated by the advance of science. However, Lovecraft would probably be more in sympathy with Old Ones-worship, because it at least was based on a real though erroneous conception of real (in the weird tale context) aliens – unlike theistic worship which, according to Lovecraft, has no evidential basis whatsoever.