You are correct Ancestry doesn't allow DNA tests taken with another company to be uploaded. It's a shame he didn't go with Ancestry.

I had mine done with Ancestry and uploaded to MH and the ethnicity results on MH are different to Ancestry - MH have picked up some other DNA but I assumes what MH picked up is included in Ancestry's England, Wales & Northwestern Europe label and I have picked up quite a few Swedish and Finnish 4th cousin connections on MH but I suppose that is because they aren't members of Ancestry.

But I don't think 25% is that much to be honest and could be a fair way back but I am a novice. I expect my Scandinavian/Finnish DNA on MH to be way way back but again who knows. DNA filters through unexpectedly it seems.

My Heritage:

North and West Europe - 98.4%
Irish, Scottish, and Welsh - 72.9%
Scandinavian - 23.2%
Finnish - 2.3%
East Europe - 1.6%
Baltic - 1.6%

and Ancestry is this:

* England, Wales & Northwestern Europe 50%
* Scottish Lowlands, Northern England & Northern Ireland

* Ireland and Scotland 50%
* Scottish Central Lowlands