Vlachs and Greek Orthodox Albanians in Greece?
Neither of these groups is remotely comparable in numbers to the Macedonians.
Vlachs and Greek Orthodox Albanians in Greece?
Solidarity/common self-identification is the essence of a national identity (in the modern sense). Language doesn't have to be a barrier to that, but for obvious reasons it often is.
Vlachs and Arvanites in Greece were IIRC heavily mixed with the Greek majority, and spoke Greek to a significant degree even before they fully assimilated. Also, they were a part of the Greek revolution and Greece itself from the start - this no doubt helped entrench the whole solidarity/commonality thing necessary for peacefully and naturally adopting a national identity.
Meanwhile the Bulgarians/Slavs in general in Macedonia lived alongside a Greek population only in certain sub-regions; in others they'd have no prior experience and mingling with the Greek language. The Phanariotes would be another disadvantage: those communities in the Balkans which did not live near Greeks often had an unfairly negative stereotype of them, since in the limited experience of these communities, Greek meant the widely disliked Phanariotes and unpopular upper clergy.
If the Slavs in Macedonia somehow get involved in the Greek revolution and end up in early Greece, a large minority could adopt a Greek identity of sorts (but probably not the majority and definitely not all). Other than that, not sure how it could happen.