tl;dr: as of 2019, it would seem that about € 1 242 176 has been raised.

ICCF & Vim seem very intertwined, and probably a majority of the donations came from Vim users, but there is no way anyone can be certain about this.

Full answer:

The ICCF has published financial reports from 1998 through 2013.

'94-'96 € 5 000 (estimate) 1997 € 7 241 (ƒ15 958) 1998 € 10 010 (ƒ22 060) 1999 € 15 122 (ƒ33 326) 2000 € 17 333 (ƒ38 198) 2001 € 26 441 2002 € 29 258 2003 € 28 625 2004 € 29 262 2005 € 36 937 2006 € 46 163 2007 € 47 688 2008 € 46 050 2009 € 50 309 2010 € 47 297 2011 € 54 790 2012 € 50 150 2013 € 55 595 2014 € 73 350 2015 € 68 872 2016 € 62 558 2017 € 65 562 2018 € 69 790 2002 .de € 10 140 (estimate) 2003 .de € 9 920 (estimate) 2004 .de € 10 140 (estimate) 2005 .de € 12 799 (estimate) 2006 .de € 15 995 (estimate) 2007 .de € 16 523 (estimate) 2008 .de € 15 955 (estimate) 2009 .de € 17 430 (estimate) 2010 .de € 16 386 (estimate) 2011 .de € 18 981 (estimate) 2012 .de € 17 373 (estimate) 2013 .de € 19 259 (estimate) 2014 .de € 25 421 (estimate) 2015 .de € 23 867 (estimate) 2016 .de € 21 679 (estimate) 2017 .de € 22 720 (estimate) 2017 .de € 24 185 (estimate) Total € 1 242 176

The German donations are mentioned separately. The 2002 report mentions:

Most sponsors and donors from Germany started paying through MISEREOR in 2002. This gives them a tax advantage. In 2002 about 10 140 euro has been received by MISEREOR. This money goes directly to the project and can therefore not be found in the ICCF Holland figures. When adding MISEREOR to the total amount that sponsors and donors have contributed towards the project, the increase is almost 50%.

And the report from 2003 and onwards either don't mention a figure, or mention a figure of "more than 10 000". I've grown this amount with the same amount as the other donations for 2003 and onwards, which should give a reasonable-ish estimate. Bram has mentioned these are slightly too high after I announced that about a million Euro had been raised:

The estimate for the German donations are a bit too high though. Last year [2016] was about 16 000 euro.

So how long has Vim been involved with ICCF? The oldest version of Vim I've been able to find if Vim 3.0 from March 1996 (here); this already has the "charityware" license, in the uganda.txt it says:

Summer 1993 I spent one month in Uganda with a Dutch team. I was very impressed with what I experienced there. Together with local people we built a nursery school in Kibaale. In only three weeks from nothing to a roofed building! [..] The work is very well organized. Every dollar is spent on something useful. Our team brought about $2000. [..] How do you know that the money will be spent right? First of all you have my personal guarantee as the author of Vim. Further the project is co-sponsored and inspected by World Vision, Save the Children Fund and International Child Care Fund. I will work for the project as a volunteer from September 1994 to August 1995.

I don't have the figures from 1994 to 1996; based on the above figures, I'll add an estimate of €5 000 for these 2 years.

So how much of this money comes from Vim users? All the financial reports have a statement similar to this one:

Donations have been received for the use of Vim, but this is not mentioned separately, because it is not always clear if a donation was because of using Vim.

This makes sense. I once did a (one-time) donation to ICCF, and just transferred some money to the bank account; there is no way to know that I donated because I use Vim and read about Uganda there.

The announcement of the 2014 financial report also mentions:

I am very glad to see the amount has gone up quite a bit. Mostly because of one-time donations. I'm not sure this is because of Vim users, but I expect so

Vim does keep a "hall of honours" of people who donated more than €100; however, this list is probably very incomplete as well. The total amount listed here is about €25 000. But for many people the donation amount is concealed, and there are probably many more who aren't listed at all. So for the purpose of this question, it's not very useful.