Yes. You have two options:
RTMP mode: via the "Stream" option
Webcam mode: either via "External Video" or via NDI
Loola RTMP Mode:
Open the stream settings in vMix:

Copy and paste the RTMP URL and Key from the Loola Studio to vMix:

Configure the Quality/Encoder settings:

See recommended platform encoder settings here:
https://support.loola.tv/en/articles/3284585-rtmp-encoder-settings
Click the Stream button in vMix to start the preview in Loola:

Loola Webcam Mode
vMix External Video (virtual camera)
First, make sure that "vMix Video / Streaming" is checked in the vMix settings.
Note: in order to support vertical 1080p (720x1280) in Loola, set the output height in vMix to be equal or larger than 1280:

Next, click the "External" button in vMix:

Next, select vMix in Loola and set desired resolution:

Note: the integral vMix Virtual Camera driver support video only. To get audio out of vMix, see the NDI option below.
vMix and NDI:
The video/audio flow: vMix --> NDI --> Loola --> Social Platforms
Start by with enabling NDI output in vMix:

More details here:
https://www.vmix.com/help21/index.htm?SettingsOutputs.html
Next, run the NDI Virtual Input:

Next, configure NDI to show the vMix output.

Next, select NDI audio and video sources in Loola:
