The essential ethical question that animates the story in each case is "What is man's role in nature (and does that role extend to the creation of life)?"
This is a question of power, of natural order, of ambition and of man's reach. What happens when he reaches too far and plays with forces he does not completely understand?
The Greek myth of Icarus deals with the same themes.
I love the quote by Ian Malcolm from the movie that goes something like "...you were in such a hurry to see if you could that you didn't take the time to wonder if you should." I think both stories focus on the dangers of science without conscience. Such an interesting point in connecting the two.
Both Jurrassic Park by Michael Chrichton and Frankenstein by Mary Shelley are extreme examples of science being misused or used to indiscriminately. Both books deal with scientific theory run amok and the repercussions of such events.
What happens when we try to tamper with nature? In both stories, monsters are created by artificial means, and the consequences are not good, are they? No one in either story sets out to create a monster, certainly, but look at what happens in each case. In both stories, the attempt to manipulate nature is done through "science," and the "scientists" have not considered the possible outcomes to tampering with nature and have disregarded the ethics of the situation. This theme, of mankind trying to improve on nature, is both ancient and new. As we speak, scientists must consider the ethical and practical consequences of cloning, stem cell use, and medications that can alter the brain. Both stories grapple with these issues in a way that makes a strong point about this theme.
I think the two are connected because moinsters were formed by artificial ways of life. With that being said they were not naturally made and both monsters caused major problems problems.