Clean/cultured meat doesn't harm any animal and is grown industrially.
Could clean/cultured meat fit into a Vegetarian's diet? Cultured meat's an animal product created using animal cells and therefore it can't fit into a vegan's diet.
There is no official body dictating what vegetarians may and may not eat. Each needs to make his or her own decision. I don't think that I would eat it since I am quite happy with traditional vegetarian options. However, if meat eaters switch to it then I would be pleased.