First of all, the two verbs in question (is and marries) do not necessarily have to be in the same tense, so it is possible to change one or the other of them independently of the other. Let's look at them one at a time. The first part is actually pretty straightforward:
Their collaboration is important
This says that their collaboration is important now, whether or not it was important in the past.
Their collaboration was important
This says that their collaboration was important in the past, but does not say anything about whether it is still important now.
The second bit is a bit trickier:
it marries the artist with the scientist
Arguably, this really should be in the past tense to begin with, because "it" (their collaboration) is something that took place in the past, so anything that it did (marrying the artist with the scientist) should also have taken place in the past:
it married the artist with the scientist
I suspect the reason why the author put this in the present tense is actually because they were actually intending to speak about "collaborations like this one" in general, instead of that one specific collaboration. Since "collaborations like this" are things that (it is implied) go on all the time, it is common to talk about such things in the present tense. However, in this case, unfortunately, that is not actually what the subject of the sentence was written as (it was actually "their collaboration", not "collaborations like theirs"), so what they wrote is technically wrong (though not in a way that probably causes problems for most readers).
So regarding the case of marries, it should probably either be:
Their collaboration is important because it married the artist with the scientist.
Collaborations like theirs are important because they marry the artist with the scientist.
(Again, even when talking about "collaborations like theirs" you can also use either "are important" or "were important" depending on whether you mean to say that they are important now, or they were important in the past, but it does not affect what form of "marry" you use.)