As far as I know, the Riddle House is owned by some random property investor (for lack of a better term) who bought it for, as your question says, tax purposes. I don't think it was a Death Eater because Voldemort took great care to hide his Muggle paternity from the world -- even in Order of the Phoenix, Bellatrix Lestrange is shocked at Harry's assertion that Voldemort is a half-blood.
‘Yeah,’ said Harry, maintaining his tight grip on the glass ball, expecting another attempt to bewitch it from him. ‘Yeah, I’ve got no problem with saying Vol—’
‘Shut your mouth!’ Bellatrix shrieked. ‘You dare speak his name with your unworthy lips, you dare besmirch it with your halfblood’s tongue, you dare –’
‘Did you know he’s a half-blood too?’ said Harry recklessly. Hermione gave a little moan in his ear. ‘Voldemort? Yeah, his mother was a witch but his dad was a Muggle – or has he been telling you lot he’s pure-blood?’
A jet of red light had shot from the end of Bellatrix Lestrange’s wand, but Malfoy had deflected it[.]
Order of the Phoenix - pages 691-692 - Bloomsbury - chapter thirty-five, Beyond the Veil
There is no indication in the books, in any JKR interview that I know of, or at Pottermore that would suggest anyone other than a wealthy Muggle owns the Riddle House. From Pottermore: