Hey all! I have another kind of odd name to ask about. I've heard two or three definition variations and roots for this rather rare surname.

The most common it seems would be the Irish origin of it.
The name Hyland is of Irish origin Irish: from the Anglicized form of Gaelic Ó hAoileáin, a variant of Ó Faoláin (see Whelan) from the Irish word faol, meaning wolf. Other anglicisations include Phelan.

Interesting how it can go from "Ó Faoláin" to "Hyland" like that. So, is "Ó hAoileáin" pronounced like "oh high-lan"? and is Ó Faoláin pronounced like "Whelan"?

And does anyone know how "hAoileáin" can mean "wolf" when wolf is supposed to be faol? Is it a phonetic thing?

Aoileán doesn't mean "wolf" (h- and -áin are just grammatical changes). Faol means (meant) wolf, faolán was a little wolf.
It is common, even in Irish, that the meaning of names becomes obscure. So, Aoileán could mean nothing.

Ó Faoláin -> Ó hAoláin -> Ó hAoileáin .
F is pronounced bilabially in Irish. A somewhat weak sound. It is totally mute if lenited (i.e. f->fh) (e.g. genitive Uí Fhaoláin, female Ní Fhaoláin) So, if you only know the lenited variant (pronounced "Aoláin") you can't tell what is the unlenited variant (Ó Faoláin / Ó hAoláin) And voilà: a new name is born.
Loss and insertion of f- is common in Irish (e.g. oscail / foscail = to open)

Ao is pronounced different in Irish regions. Like "ay", "ee" or (unrounded) "oo". Perhaps some more pronunciations existed in history.
Furthermore: Anglicized versions (e.g. "Hilane") change over time and place due to different pronunciations of varying spellings. So "Hyland" isn't surprising at all.

There is a town in Leitrim called 'Mohil' (Maothail) and if the Irish spelling and the real English pronunciation (not the one off the TV and radio with the long o), it might have been a short [ɨ] or [ɯ] once (which I guess is different to the long one that survived into dialect study times)

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According to MacLysaght, in his The Surnames of Ireland, (O) Hyland is "[u]sually a form of Ó Faoláin (Phelan). It has become Ó hAoileáin in Connacht, where it is sometimes synonymous with Whelan. In England (but not in Ireland) Hyland is a variant of Hayland." That seems to indicate that the Ó Faoláin ("descendant of the little wolf") form is the original.

MacLysaght also has a listing for (O) Hilan which states that it is "[u]sually a variant of Hyland in Cos. Kilkenny and Kildare but it has been used for Filan in Westmeath." And, in another listing for (O) Hillan[d}/Hillen, he says that it "is occasionally a variant of Hilan; but in Ulster, where they are mainly found, Hillan and Hillen are of English origin."

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

Thanks for the info, that's very interesting about the grammatical changes over time! So, Hyland ... Does? Or doesn't(?) Mean wolf?