Can a non Catholic participate in Ash Wednesday services?

yes my friend did by the way it depends if they want to!
Yes!

On Ash Wednesday the imposition of Ashes, a sign of repentance, is a sacramental, not a sacrament. Sacramentals, like holy water or being blessed by a priest, are open to all. The non-Catholic should be sure though, that if they are receiving ashes, to respect what this means. Ashes are a sign of repentance at the start of the holy season of Lent, a season where we prepare for Easter, the holiest of seasons, by prayer and fasting. Do not get ashes unless you intend to do prayer and fasting in repentance of your sins.

Sacraments, on the other hand, are only open to believers. Baptism is only open to those who wish to become Catholics, or infants whose parents intend to raise the child in the Faith. Reconciliation or confession is open only to Catholics for the forgiveness of sins, though protestants planing to enter the Church, called candidates receive this sacrament before their first communion (unbaptized persons entering the Church, called catechumens, have no need as sin is forgiven during baptism). Conformation is only given to a Catholic or one entering the Catholic Church. Sacramental marriage is open to all baptized Christians without impediments (prior marriage, religious vows of chastity or celibacy, clinical impotence), though one of the spouses must be Catholic in order to be married in a Catholic Church. Ordination is only open to Catholic men without impediments (in the west, marriage), and lastly the anointing of the sick is only open to Catholic. With Baptism, Communion, confession and the Anointing of the Sick, however, one can be received into the Church and receive these sacraments immediately in danger of death (e.g., a man who intends to become Catholic gets into a fatal car crash and a priest comes to the hospital, before the man dies, the priest can do these things).