Yes, Siberian roe are a different sub species of Capreolus and I have also heard of hybridisation on the fringes of their range. I have never heard of any being released in the UK though. I guess the main problem is, as happened with other strains of imported reds and Wapiti when tried here - the genes are very quickly diluted.
I think feeding/climate (associated factors) affects size/quality more than strain (ref Oz/NZ) as proven when English park reds were released on the hill in Scotland in the 19 century and the animals 'blended in' often after a year or so.
Nick
The issue of red deer and their genetics is interesting. A lot of reds from English parks were introduced to various Scottish deer forests in the 19th/20th centuries to improve the weights and antlers, over 30 forests received Warnham blood, and in general you're correct in that the beneficial effect was in the long term at best muted if not absent, and I agree that this was probably the effect of the poor environment on the open hill. When these deer accessed the newly forested areas like Galloway, all of a sudden there are much bigger heads turning up, which must be the genetics kicking in given decent feeding.
The wild deer in many English and Welsh areas are from park origin and as we know they often have superb antlers and big body weights in many cases. The best antlers in the UK are probably from Warnham Park stock and if you look at the history of the escaped populations in many cases, including Norfolk/Suffolk you can trace it back to Warnham.
The New Zealand reds trace back to two basic original genetic lines, Invermark (Scottish) and English park deer (Woburn and Warnham), and in his books D. Bruce Banwell points out the differences in antler formation with the Invermark deer having classic "royal" characteristics with brow, bey and tray each side with the additional tines in a cup formation on top. Having said that, we know that many Scottish reds have English park blood in them so the Invermark deer may not have been pure Scottish reds. The monstrosities produced in some parts of NZ probably trace back to English park deer with additonal blood from East European maraloid reds and wapiti. I have been watching some clips from a NZ outfitter called Gary Herbert and the massive reds he produces for clients are aesthetically horrible.
I think environment certainly has something to do with it but given good feeding the genetics will kick in and the antler production reflects this. A good example is East Anglia where the reds originate from very good quality English park stock and this is reflected in the current population which produces the majority of UK CIC medals whereas the roe in East Anglia have a German heritage (they were introduced in 1884) and even with the influx of better quality roe from outside East Anglia the area still produces very few medal roe. The area populated by the two species overlaps, so if it were just down to environment alone you'd expect either good or poor heads from both.
As a final point, if genetics are not a factor why do almost all deer managers "leave a good buck/stag in" for it's useful breeding life if it isn't to capitalise on good genetics?
Obviously the "r" was a typo.