It really depends when one talks about an off-meta pick in a role. Speaking as a support main, who is willing to experiment, it seems that there is the off-meta pick and off-off-meta pick.
For example, Galio support is an example of the first type (not a popular champ for support but can do the support role pretty darned well - shield, ccs and movement speed boosts for the adc). Even Heim, Veigar, Elise and Ahri can fit in this grouping. (All of these have been used as support in diamond+ play in the last year effectively.)
Then there is Teemo support as an example of the second type. Not only is he not meta, but he has risks of ks and/or minion steal with little to no trade off in exchange for the weak protection for the adc (i.e., little to no: shields, enemy slows, enemy ccs). Granted, the effects of the Q and E are nice but they tend to be a bit more skill shot related and not directly benefiting the adc. And let's not forget that the shrooms tend to pinch minions away from the carry.
Plus, I hate to say it but usually when I get another position on the Rift, and I see a Teemo support on my team, I worry. I rarely see support items used, little to no warding (often due to a lack of sightstone itemization) and little to no utility items.
Despite this, I have no problem with a Teemo player in the support role - but if you do play him, then please play him as an actual support. And please not in my ranked games. :)