Another search phrase that I thought I could answer!
Yes, IAG will work with VASCO!
VASCO Middleware and Identikey use the RADIUS protocol, and RADIUS can be configured as one of the authenication methods on IAG.
You will need to define the VASCO server, along with the correct ports and shared secret.
I would configure Windows AD authentication and VASCO, so the user would need to login with AD username, AD password and VASCO one time password.
In the past, I have installed VASCO Middleware on the IAG appliance, but this would be subject to the number of users/tokens required. Unless you are looking at single figures of VASCO tokens, I would recommend that the VASCO server be installed somewhere else.