The European Commission has objected to the deal, citing possible competition constraints on the MySQL database – which is owned by Sun – after the proposed takeover, but it said in December it was optimistic a "satisfactory outcome" was possible.
The commission has until 27 January to decide on the deal.
MySQL has been a rare major newcomer to the global database market – dominated by technology heavyweights Oracle, IBM and Microsoft – pushing down prices of databases and maintenance.
Widenius launched an internet campaign to collect signatures in response to Oracle mobilising its big customers to tell European Commission hearings last month that the potential takeover was not anti-competitive.
Competition lawyers have said enlisting major firms to express support could sway regulators.
Widenius, one of the most respected developers of open-source software, left Sun last year to set up his own small database firm Monty Program Ab.
Sun – which employs about 500 staff at Linlithgow in West Lothian – bought MySQL for $1bn in 2008.
Widenius said: "Our signatories don't have faith that Oracle could be a good steward of MySQL."
The campaigners said more than 5,000 signatures are from self-employed developers and more than 3,000 from employees of companies and organisations of all sizes using MySQL.
The signatures were delivered to the European Commission, the Chinese ministry of commerce and the Russian federal Antimonopoly Service.