EDIT2
Scala Now in the IDE there is support for templates with type inferences, semantic highlighting, etc. for the Play platform from version 3.0 IDE. The same goes for route files, woohoo; -)
Not sure about support for Play, Scalate, or other template engines in IntelliJ.
CHANGE
Play 2.0 is incredibly large, so much so that the lack of IDE support is quite insignificant - all the heavy lifting is done using the model, controller and javascript levels (coffeescript + datatables); view layer consists of simple xhtml-skeletons, so no biggie that has, for example, autocomplete for Scala code - your application will not compile if there are errors, regardless of whether you are safe to download; -)
If and when support for the IDE of the template level will be supported, this will be a pleasant addition, but nothing that I personally will not lose sleep ...
ORIGINAL
Just discovered something last night after a couple of months of relative joy breaking into Scala -IDE for Eclipse:
It seems that there is no support for any level of the template (code completion, syntax highlighting, etc.). This is true even for the new TypeSafe adapter, Play 2.0, with Razor style @ syntax. Scalate, the same boat, none of the uber cool options (jade, ssp, scaml) are recognized by the IDE.
This is not only the case for Scala -IDE, which seems to apply to IntelliJ as well, about 2 years after requesting template support:
http://youtrack.jetbrains.com/issue/SCL-1876
Obviously, it is difficult to implement, otherwise we will have built-in support for plug-ins for the main template languages. Here, it seems to me that the best I could do was get the IDE to interpret the .jade extension as Scala code that highlights Scala keywords in a nice blue and nothing else, without hangs, code completion, arrgggghhh; -)
? Groovy/Grails, IDE Scala , .