Is it possible to create a Vaadin project in Eclipse without installing the Vaadin plugin?
Yes,
just use the maven build system for this. You will then have to open the maven project in eclipse, there are tutorials for this as well.
How to create a maven vaadin project
mvn -B archetype:generate \
-DarchetypeGroupId=com.vaadin \
-DarchetypeArtifactId=vaadin-archetype-application \
-DarchetypeVersion=8.3.0 \
-DgroupId=org.test \
-DartifactId=vaadin-app \
-Dversion=1.0-SNAPSHOT \
cd vaadin-app mvn package jetty:run