Whether ancestor veneration counts as worship has been a consequential question rather than an academic one, and the same institution has answered it in opposite ways at different times.
The Chinese Rites Controversy turned on it. Jesuit missionaries in China from the late sixteenth century argued that the ancestral rites, and the honours paid to Confucius, were civil and social observances expressing filial respect rather than acts of worship, and could therefore be permitted to converts. Dominican and Franciscan missionaries argued the opposite. Rome ruled against the Jesuits in 1704 and again in 1715; the Kangxi emperor responded by expelling the missionaries who accepted the ruling, and the mission never recovered its position. The Catholic Church reversed itself in 1939, permitting the rites as civil honours, which is what the Jesuits had said two and a half centuries earlier.
The question cannot be settled by observing behaviour, because the behaviour is compatible with both readings and because participants themselves differ. Many will say plainly that they do not think anything resides in the tablet and that the rite is remembrance and respect. Others speak of ancestors acting, intervening, requiring and punishing, and consult them before decisions. Both accounts are given inside a single family, sometimes by people kneeling side by side.
The comparative lesson is that the worship-or-honour distinction is a category imported from a tradition that needed one, having a jealous God and a doctrine of idolatry. Applied to a practice built on kinship obligation rather than on divinity, the question can certainly be asked, but it does not necessarily have an answer, and insisting that it must have done a great deal of historical damage.