Mixing Yeast Strains?

Is it possible to mix yeast strains when pitching?

I have this extra WhiteLabs Trappist Ale yeast vile sitting around. I'm considering brewing up another high grav. belgian, and will more than likely have a vile of WhiteLabs Belgian Ale yeast at my disposal too. Is it possible to mix the two yeast strains upon pitching? Is there any reason that I shouldn't do this?

5gB

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WLP575 Belgian Style Ale Yeast Blend
A blend of Trappist type yeast (2) and one Belgian ale type yeast. This creates a versatile blend that can be used for Trappist type beer, or a myriad of beers that can be described as 'Belgian type'.

The only problem I've seen when mixing strains is the yeast flocculating like a box of rocks because the two strains stick to each other. I doubt you'll have that problem with those two.

I've mixed and ale with a lage yeast.

I let it ferment for about 24 hours at room temp then place it in the cold for a couple more days. Bring it back inside and record some specs and rack if the gravity is down. Place the carboy back into the cold for another week or 2.