When there is incomplete dominance of one allele, is one allele still considered recessive?
No - if we have a phenotype, in your case the tail, which we can measure and treat as a numeric variable, and if a heterozygote's phenotype is exactly half-way between that of the two homozygotes, the phenotype is considered not to exhibit. Dominance exists only when the heterozygote's phenotypic value lies closer to one homozygote than the other.