Så vidt jeg ved, kommer deltageren i morgen.

Normally, yes: in a simple main clause, Danish often has subject + verb:

Deltageren kommer i morgen.
= The participant is coming tomorrow.

But here the sentence begins with Så vidt jeg ved. When something other than the subject comes first in a Danish main clause, the finite verb usually moves to the second position. This is a basic Danish word-order rule, often called V2.

So:

• Så vidt jeg ved = first element
• kommer = verb in second position
• deltageren = subject after the verb

That is why the sentence is:

Så vidt jeg ved, kommer deltageren i morgen.

Så vidt jeg ved is a very common expression meaning something like as far as I know.

It tells the listener that the speaker is not claiming absolute certainty. It works as a kind of comment on the whole sentence that follows.

So the structure is roughly:

• Så vidt jeg ved = speaker’s limitation of knowledge
• kommer deltageren i morgen = the actual statement

It is a fixed, natural expression in Danish, and learners should treat it as a useful chunk.

Deltageren is the definite singular form of deltager.

• en deltager = a participant
• deltageren = the participant

In Danish, definiteness is often added as a suffix at the end of the noun instead of using a separate word like English the.

So -en here means the.

This also tells you that the sentence is talking about a specific participant, not just any participant.

Danish often uses the present tense to talk about the future when the time is clear from context.

Here, i morgen already shows that the action is in the future, so kommer is perfectly natural.

Compare:

• Han kommer nu. = He is coming now.
• Han kommer i morgen. = He is coming tomorrow / He will come tomorrow.

English can also do this in some cases, so the idea is not completely foreign.

In standard modern Danish, it is written as two words: i morgen.

So the correct spelling is:

Så vidt jeg ved, kommer deltageren i morgen.

You may sometimes see older or nonstandard spellings, but for normal modern written Danish, use i morgen.

Yes, in normal Danish punctuation, the comma is expected here.

Så vidt jeg ved functions as an introductory clause/expression before the main clause:

Så vidt jeg ved, kommer deltageren i morgen.

Danish comma rules can be a bit tricky, but in a sentence like this, the comma helps separate the introductory part from the main statement.

Yes, that is possible.

It means essentially the same thing, but the rhythm and emphasis are a little different.

• Så vidt jeg ved, kommer deltageren i morgen.
  This starts with the uncertainty marker right away.
• Deltageren kommer i morgen, så vidt jeg ved.
  This gives the information first, then adds as far as I know.

Both are natural, but the original version is especially common when the speaker wants to be cautious from the beginning.

Yes. Danish allows quite a lot of movement of sentence elements, but the verb still stays in second position in the main clause.

For example:

I morgen kommer deltageren, så vidt jeg ved.
or
I morgen kommer deltageren.

Notice that when i morgen comes first, the verb kommer still comes before the subject deltageren.

You would not say:

I morgen deltageren kommer
because that breaks the normal main-clause word order.

It is best to learn it as a set expression.

You can analyze it word by word, but for most learners, the most useful thing is to remember the whole phrase:

så vidt jeg ved = as far as I know

That will help you produce natural Danish more easily. It is one of those expressions that native speakers use very often, so it is worth memorizing as a chunk.