If I've understood, the known archaeologists in Julian's camp are Mike PP, who is said to have mentioned it in a talk, and a research group who have issued a very strong report to a WHS Steering Group. There may be other professional archaeologists who have not said anything as yet.

Oh go on then, here's a few professional archaeos who have published pieces against the proposed tunnel:

Dr George Nash https://heritageaction.wordpre[...]enge-tunnel-another-viewpoint/

Dr Rachel Pope https://twitter.com/preshitorian

Professor Dan Hicks: http://www.independent.co.uk/n[...]ing-dont-bury-it-a7543226.html
http://theconversation.com/arc[...]t-of-stonehenges-setting-71451

Penelope Foreman (less unequivocal, but still "anti-tunnel"): https://suspiciousmounds.wordp[...]m/2017/01/17/under-stonehenge/

There are plenty of others who are lending support to the Save Stonehenge campaign (Dr Matt Pope, Dr Kenny Brophy, etc). Most of the ones with links to EH/NT are saying nothing, rather than coming out in support of the scheme.