The fact that the compost is ericacous won't affect the seeds, but the compost will be much too strong. Try mixing it with the same volume of coarse sand.

Most veg need a neutral to slightly alkaline base. I wouldn't use ericaceous at all, but a soil based compost such as John Innes No.3 mixed with garden/kitchen compost. The acid content of the ericaceous may well burn seedlings, in the same way that alkaline/lime soil burns azaleas, camellias etc. Beans, peas etc, will love the added garden/kitchen compost. I have been told that lettuce successfully grown in a slightly acid soil, has a stronger flavour, like spinach!! But not tried this myself as I prefer to retain the individual flavours of each salad.