Beats me. Only Jesus knows who are his. He gave us hints though:
Mat 7:15 "Beware of false prophets, who come to you in sheep's clothing, but inwardly they are ravenous wolves.
Mat 7:16 You will know them by their fruits. Do men gather grapes from thornbushes or figs from thistles?
Mat 7:17 Even so, every good tree bears good fruit, but a bad tree bears bad fruit.
Mat 7:18 A good tree cannot bear bad fruit, nor can a bad tree bear good fruit.
Mat 7:19 Every tree that does not bear good fruit is cut down and thrown into the fire.
Mat 7:20 Therefore by their fruit you will know them.
Mat 7:21 "Not everyone who says to Me, 'Lord, Lord,' shall enter the kingdom of heaven, but he who does the will of My Father in heaven.
Mat 7:22 Many will say to Me in that day, 'Lord, Lord, have we not prophesied in Your name, cast out demons in Your name, and done many wonders in Your name?'
Mat 7:23 And then I will declare to them, 'I never knew you; depart from Me, you who practice lawlessness!'
Christ indicates that there will be MANY who will claim to follow him but their lawlessness, their sin, the antipathy of the law of God, will mark them out.
Paul says much the same thing though in a different way:
Gal 5:19 Now the works of the flesh are evident, which are: adultery, fornication, uncleanness, lewdness,
Gal 5:20 idolatry, sorcery, hatred, contentions, jealousies, outbursts of wrath, selfish ambitions, dissensions, heresies,
Gal 5:21 envy, murders, drunkenness, revelries, and the like; of which I tell you beforehand, just as I also told you in time past, that those who practice such things will not inherit the kingdom of God.
Gal 5:22 But the fruit of the Spirit is love, joy, peace, longsuffering, kindness, goodness, faithfulness,
Gal 5:23 gentleness, self-control. Against such there is no law.
Christianity today, as I'm sure you will agree, is chock full of those who claim Christ yet practice and espouse all sorts of lawlessness. Whether or not they embrace the tradition of the trinity matters little at that point.
All other factors being equal does it matter? Does it matter if their beliefs concerning who Christ is are trinitarian or whether they more closely resemble those described as Unitarianism, Arianism, Docetism, Nestorianism, Modalism, Subordinationism, Sabellianism… etc.?
Or is the only thing that matters is they do not "espouse all sorts of lawlessness" according to the United Church of God and its adherents.