Yes Scotland has some very easy donation rules: Anybody can donate up to £500 (even people who have absolutely no connexion to Scotland), but to donate more than that you need to be domiciled in Scotland. Fair and easy.
On the other hand, Better Together's donation rules really are somewhat difficult to comprehend. They seem to be happy to allow donations from the rest of the UK, but possibly only from "real Scots", as they like to call them:
Let's have a look at all the Better Together boxes:
- It's clear Better Together will accept unlimited donations from "real Scots" living in Scotland.
- They haven't said much about donations from "foreigners" in Scotland. It's possible that they (like the SNP and Yes Scotland) consider everybody living here to be Scottish, in which case they'll allow unlimited donations from this source, too.
- I've written "unlimited" in this box because otherwise there's no way that Ian Taylor (born, educated and domiciled in England, but with Scottish ancestry) would have been allowed to donate £500k.
- I'm basing this on this quote from The Herald: "Better Together campaign director Blair McDougall [...] said he would refuse to take cash from foreign donors, but would accept UK-wide donations up to £500."
- Better Together's website contains this: "we will ask all donors to confirm they are not from overseas; we will check that anyone who gives a donation of over £500 is not from overseas". So people from abroad can still donate up to £500 if they pretend to live in the UK.
- Same as above. It appears Better Together don't differentiate between "real Scots" and "foreigners" when they live outwith the UK.